U.S. patent application number 12/578219 was filed with the patent office on 2010-05-06 for anti-reflective coatings comprising ordered layers of nanowires and methods of making and using the same.
This patent application is currently assigned to Nano Terra Inc.. Invention is credited to David Christopher COFFEY, Brian T. Mayers, Joseph M. McLellan.
Application Number | 20100112373 12/578219 |
Document ID | / |
Family ID | 42101266 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100112373 |
Kind Code |
A1 |
COFFEY; David Christopher ;
et al. |
May 6, 2010 |
Anti-Reflective Coatings Comprising Ordered Layers of Nanowires and
Methods of Making and Using the Same
Abstract
The present invention is directed to anti-reflective coatings
comprising ordered layers of nanowires, methods to prepare the
coatings, and products prepared by the methods.
Inventors: |
COFFEY; David Christopher;
(Boulder, CO) ; Mayers; Brian T.; (Somerville,
MA) ; McLellan; Joseph M.; (Quincy, MA) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Nano Terra Inc.
Cambridge
MA
|
Family ID: |
42101266 |
Appl. No.: |
12/578219 |
Filed: |
October 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61104438 |
Oct 10, 2008 |
|
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Current U.S.
Class: |
428/608 ;
156/272.2; 156/60; 156/89.11; 427/331; 427/336; 427/372.2; 427/532;
427/535; 427/551; 428/113; 428/212 |
Current CPC
Class: |
B82Y 20/00 20130101;
Y10T 428/249953 20150401; B32B 33/00 20130101; G02B 2207/101
20130101; Y10T 156/10 20150115; Y10T 428/24124 20150115; G02B 1/118
20130101; Y10T 428/24942 20150115; Y10T 428/12444 20150115 |
Class at
Publication: |
428/608 ;
428/113; 428/212; 156/60; 156/272.2; 156/89.11; 427/331; 427/372.2;
427/532; 427/551; 427/535; 427/336 |
International
Class: |
B32B 5/12 20060101
B32B005/12; B32B 7/02 20060101 B32B007/02; B32B 7/00 20060101
B32B007/00; B32B 37/00 20060101 B32B037/00; B32B 38/00 20060101
B32B038/00; B32B 37/06 20060101 B32B037/06; B05D 3/00 20060101
B05D003/00; B05D 3/02 20060101 B05D003/02; B05D 3/06 20060101
B05D003/06; B05D 3/10 20060101 B05D003/10 |
Goverment Interests
STATEMENT OF GOVERNMENT RIGHTS
[0002] This invention was supported by U.S. Government Contract
Numbers NBCH1080008 and W31P4Q09C0023. The U.S. Government may have
certain rights in this invention.
Claims
1. A composition, comprising: a substrate including a surface; and
a multi-layer coating of nanowires positioned on at least a portion
of the surface, the coating comprising three or more laminar layers
of nanowires, including a bottom layer of nanowires affixed to the
surface, and a top-most layer of nanowires, wherein a nanowire
within a laminar layer is oriented substantially parallel to
another nanowire within the same laminar layer, nanowires within
adjacent laminar layers are not substantially parallel to one
another, the top-most layer of nanowires has a refractive index of
about 5% to about 70% of a refractive index of the bottom layer of
nanowires, and the refractive index of the three or more laminar
layers of nanowires decreases by about 10% or more per laminar
layer from the bottom layer of nanowires to the top-most layer of
nanowires.
2. The composition of claim 1, wherein the bottom layer of
nanowires has a refractive index of about 30% to about 100% of a
refractive index of the substrate, wherein the top-most layer of
nanowires has a refractive index of about 1% to about 40% of the
refractive index of the substrate, and wherein the refractive index
of the three or more laminar layers decreases by about 15% or more
per layer from the bottom layer of nanowires to the top-most layer
of nanowires.
3. The composition of claim 1, wherein the refractive index of the
three or more laminar layers of nanowires decreases alinearly from
the bottom layer of nanowires to the top-most layer of
nanowires.
4. The composition of claim 1, wherein the refractive index of the
three or more laminar layers of nanowires decreases linearly from
the bottom layer of nanowires to the top-most layer of
nanowires.
5. The composition of claim 1, wherein a thickness of a laminar
layer within the multi-layer coating of nanowires is approximately
the diameter of a nanowire present within the laminar layer.
6. The composition of claim 1, wherein nanowires within adjacent
laminar layers of the multi-layer coating are substantially
orthogonal to one another.
7. The composition of claim 1, wherein adjacent nanowires within a
laminar layer are spaced about evenly apart relative to one
another, and wherein a spacing separating adjacent nanowires within
a laminar layer is about 30% or less than an average length of the
nanowires.
8. The composition of claim 1, wherein the nanowires have an
average length of about 200 nm to about 5 mm and an average
diameter of about 1 nm to about 10 .mu.m.
9. The composition of claim 1, wherein the nanowires have an
average length of about 200 nm to about 5 mm and an average
diameter of about 5 nm to about 1 .mu.m.
10. The composition of claim 1, wherein the nanowires of at least
the bottom layer of the coating have substantially the same
composition as the substrate.
11. The composition of claim 1, wherein all of the nanowires
present within the multi-layer coating have approximately the same
composition.
12. The composition of claim 1, wherein the nanowires within the
multi-layer coating are not functionalized or derivatized.
13. The composition of claim 1, further comprising a molecular or
polymeric matrix surrounding the multi-layer coating of nanowires,
wherein at least a portion of the top-most layer of nanowires is
exposed.
14. The composition of claim 1, wherein a portion of the surface
having the anti-reflective multi-layer coating of nanowires thereon
reflects about 50% or less of an electromagnetic radiation having
at least one wavelength of about 180 nm to about 30 .mu.m compared
to an uncoated portion of the surface.
15. The composition of claim 1, wherein a portion of the substrate
having the multi-layer coating of nanowires thereon has a
resistance to crack propagation that is about 3 times or more than
a portion of the substrate surface that lacks the multi-layer
coating of nanowires.
16. The composition of claim 1, wherein the substrate having the
multilayer coating of nanowires thereon has a retro-reflectance at
633 nm that is at least 50% less than a retro-reflectance at 633 nm
from an uncoated substrate that lacks the multilayer coating of
nanowires.
17. The composition of claim 1, wherein the substrate having the
multilayer coating of nanowires thereon has a retro-reflectance at
one or more wavelengths from about 400 nm to about 12 .mu.m that is
at least 50% less than a retro-reflectance from an uncoated
substrate that lacks the multilayer coating of nanowires at the
same one or more wavelengths.
18. A composition, comprising: a metallic substrate including a
surface; and an anti-reflective multi-layer mat of nanowires
positioned on at least a portion of the surface, the mat of
nanowires comprising three or more laminar layers of nanowires and
including a bottom layer of nanowires affixed to the surface and a
top-most layer of nanowires, wherein the top-most layer of
nanowires has a refractive index of about 5% to about 70% of a
refractive index of the bottom layer of nanowires, and wherein the
refractive index of the three or more laminar layers decreases by
about 10% or more per layer from the bottom layer of nanowires to
the top-most layer of nanowires.
19. The composition of claim 18, wherein the substrate and the
nanowires comprise at least one metal that can be the same or
different selected from: a transition metal, a Group 13 metal, a
Group 14 metal, a Group 15 metal, an oxide thereof, or a
combination thereof.
20. The composition of claim 18, wherein a thickness of a laminar
layer within the mat of nanowires is about ten times or less an
average diameter of a nanowire present within the laminar
layer.
21. The composition of claim 18, wherein the nanowires within the
multi-layer mat are bound to the substrate and each other via
metal-metal bonds.
22. The composition of claim 18, wherein a portion of the substrate
having the multi-layer mat of nanowires thereon has a resistance to
crack propagation that is about 3 times or more than a portion of
the substrate surface that lacks the multi-layer mat of
nanowires.
23. The composition of claim 18, wherein the substrate having the
multilayer mat of nanowires thereon has a retro-reflectance at 633
nm that is at least 50% less than a retro-reflectance at 633 nm
from an uncoated substrate that lacks the multilayer coating of
nanowires.
24. The composition of claim 18, wherein the substrate having the
multilayer mat of nanowires thereon has a retro-reflectance at one
or more wavelengths from about 400 nm to about 12 .mu.m that is at
least 50% less than a retro-reflectance from an uncoated substrate
that lacks the multilayer mat of nanowires at the same one or more
wavelengths.
25. A process for preparing an anti-reflective multi-layer nanowire
coating on at least a portion of a surface of a substrate, the
process comprising: disposing on the surface a first laminar layer
of nanowires, wherein the first laminar layer has a refractive
index about 60% to about 100% of a refractive index of the
substrate; affixing the first laminar layer of nanowires to the
surface; disposing a second laminar layer of nanowires onto the
first laminar layer of nanowires; affixing the second laminar layer
of nanowires to the first laminar layer of nanowires; disposing at
least a third laminar layer of nanowires onto the second laminar
layer of nanowires; and affixing the third laminar layer of
nanowires to the second laminar layer of nanowires; wherein the
second laminar layer of nanowires has a refractive index less than
the refractive index of the first laminar layer of nanowires, and
wherein the third laminar layer of nanowires has a refractive index
less than the refractive index of the second laminar layer of
nanowires.
26. The process of claim 25, further comprising: aligning the
nanowires within the first laminar layer to orient the nanowires
substantially parallel to one another; aligning the nanowires
within the second laminar layer to orient the nanowires within the
second laminar layer substantially parallel to one another, wherein
the nanowires within the second laminar layer are not parallel to
the nanowires within the first laminar layer; and aligning the
nanowires within the third laminar layer to orient the nanowires
within the third laminar layer substantially parallel to one
another, wherein the nanowires within the third laminar layer are
not parallel to the nanowires within the second laminar layer.
27. The process of claim 26, wherein the aligning comprises at
least one of: applying a mechanical force to the nanowires,
applying a magnetic field to the nanowires, applying an electric
field to the nanowires, applying a fluid gradient to the nanowires,
and combinations thereof.
28. The process of claim 25, wherein the affixing comprises at
least one of: sintering, covalently bonding, cross-linking,
melting, encapsulating in a polymeric or molecular matrix, and
combinations thereof.
29. The process of claim 25, further comprising disposing a fourth
laminar layer of nanowires onto the third laminar layer of
nanowires, wherein the fourth laminar layer of nanowires has a
refractive index less than the refractive index of the third
laminar layer of nanowires.
30. The process of claim 25, further comprising aligning the
nanowires within the fourth laminar layer to orient the nanowires
within the fourth laminar layer substantially parallel to one
another, wherein the nanowires within the fourth laminar layer are
not parallel to the nanowires within the third laminar layer
31. A product prepared by the process of claim 25.
32. The product of claim 31, wherein the product is chosen from: an
antenna, a mirror, a window, a watch glass, a dome, a cone, a lens,
and combinations thereof.
33. A device, comprising: a substrate including a surface; and an
anti-reflective multi-layer coating of nanowires positioned on the
surface, the coating comprising three or more laminar layers of
nanowires and including a bottom layer of nanowires affixed to the
surface, wherein a nanowire within a laminar layer is oriented
substantially parallel to another nanowire within the same laminar
layer; wherein nanowires within different laminar layers are not
parallel to one another; and the bottom layer of nanowires has a
refractive index of about 30% or more than a refractive index of a
top-most layer of nanowires.
34. The device of claim 33, wherein the device is chosen from: a
display device, an optical device, a solar cell, a sensor, a
cellular device, an avionic device, a nautical device, a projectile
device, and combinations thereof.
35. A composition, comprising: a substrate including a surface; and
an anti-reflective multi-layer coating positioned on at least a
portion of the surface, the coating comprising three or more
laminar layers, each layer comprising a matrix incorporating a
different degree of porosity compared to the other layers in the
coating, wherein a bottom layer of the coating is affixed to the
surface, wherein the bottom layer has a refractive index of about
60% to about 100% of a refractive index of the substrate, wherein a
top-most layer of the coating has a refractive index of about 1% to
about 40% of the refractive index of the substrate, and wherein the
refractive index of the three or more laminar layers decreases by
about 10% or more per layer from the bottom layer of the coating to
the top-most layer of the coating.
36. The composition of claim 35, wherein a portion of the surface
having the anti-reflective multi-layer coating thereon reflects
about 50% or less of an electromagnetic radiation having at least
one wavelength of about 180 nm to about 30 .mu.m compared to an
uncoated portion of the surface.
37. The composition of claim 35, wherein the anti-reflective
multi-layer coating comprises a multitude of pores having a
diameter of about 1 nm to about 100 nm.
38. The composition of claim 35, wherein the matrix comprises one
or more polymers selected from: a polystyrene, a polysiloxane, a
polyacrylate, a polyvinylpyrrolidone, a polycarbonate, a
polyalkyleneglycol, a (styrene-ethylene-butylene) tri-block
copolymer grafted with maleic anhydride, and combinations
thereof.
39. A process for preparing an anti-reflective multi-layer coating
on at least a portion of a surface of a substrate, the process
comprising: printing on the surface a first laminar layer
comprising a first polymer and an optional second polymer; printing
on the first laminar layer a second laminar layer comprising the
first polymer and the second polymer, wherein the second laminar
layer is substantially free from solvent, and the second polymer is
present in the second layer in a higher concentration than the
first layer; printing on the second laminar layer a third laminar
layer comprising the first polymer and the second polymer, wherein
the third laminar layer is substantially free from solvent, and the
second polymer is present in the third layer in a higher
concentration than the second layer; optionally exposing the first
laminar layer to conditions suitable for removing the second
polymer from the first laminar layer while retaining the first
polymer within the first laminar layer; exposing the second laminar
layer to conditions suitable for removing the second polymer from
the second laminar layer while retaining the first polymer within
the second laminar layer; and exposing the third laminar layer to
conditions suitable for removing the second polymer from the third
laminar layer while retaining the first polymer within the third
laminar layer to provide an anti-reflective multi-layer coating
having a refractive index gradient.
40. The process of claim 39, wherein the optionally exposing is
performed simultaneous with the exposing the second laminar layer
and the exposing the third laminar layer.
41. The process of claim 39, wherein the optionally exposing is
performed prior to the printing on the first laminar layer a second
laminar layer; and the exposing the second laminar layer is
performed prior to printing on the second laminar layer a third
laminar layer.
42. The process of claim 39, wherein the exposing comprises a
process selected from: heating the laminar layer, irradiating the
laminar layer with electromagnetic radiation, irradiating the
laminar layer with an electron beam, exposing to a selective
solvent, pyrrolizing, exposing the laminar layer to a plasma, and
combinations thereof.
43. The process of claim 39, wherein the printing comprises:
coating an elastomeric stamp with a composition comprising a
pre-determined amount of the first polymer, the optional second
polymer, and a solvent to provide a coated stamp; phase separating
the polymers on the coated stamp; removing the solvent from the
composition; and contacting the coated stamp with the surface under
conditions sufficient to transfer the composition from the coated
stamp to the surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of
U.S. Appl. No. 61/104,438, filed Oct. 10, 2008, which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention is directed to anti-reflective
coatings, methods for making the anti-reflective coatings, and
products prepared by the methods.
[0005] 2. Background
[0006] Optical reflections occur when light passes from one medium
to a second medium when the refractive index ("n") of the two media
differs. Thus when light passes from air (n=1) to glass (n=1.5)
there are reflections. Reflections can be minimized or eliminated
by gradually grading the index of refraction from a first material
to a second material. In theory, for a single-layer coating on
glass in air, the optimum material has a refractive index of
n=1.23. While most layered coatings can exhibit small differences
in the refractive index between materials or between layers of a
coating, multi-layer films can reduce this problem. However, few
solid materials are known having a refractive index, n<1.2; and
few robust materials are known having a refractive index, n<1.3.
Thus, all presently known thin layer coatings suffer from an abrupt
decrease in refractive index at the coating-air interface that
gives rise to reflection of electromagnetic radiation from the
top-most surface of the substrate.
[0007] One method to minimize reflection from a surface is to
include single- and multi-layer thin films that incorporate
destructive interference. However, destructive interference does
not work well for incoming light not perpendicular to the
surface.
[0008] A second theoretical solution to providing anti-reflection
is to provide a porous nanostructured laminar Gradient Refractive
Index ("laminar GRIN") coating in which the porosity of a coating
material is controlled on the nanometer scale to achieve refractive
index values from n=1.0 to about n=1.4. For example, a glass
material having a refractive index, n=1.5, that is made 80% porous
will have a refractive index, n=1.1, so long as the length scale of
the porosity within the porous glass material is small enough to
avoid light scattering. In an ideal system, the refractive index
would be controllably decreased from n=1.5 to n=1.0 by controllably
increasing the volume fraction of air within the material. However,
ideal laminar GRIN structures have yet to be made using thin, solid
films.
[0009] The natural world is also replete with examples of
anti-reflective structures. For example, the surface of a moth eye
is covered with domes having a height and radius of about 150 nm to
250 nm, which provide excellent antireflective properties across
the visible spectrum.
[0010] The fabrication of nanostructured films that are similar to
an ideal theoretical or a naturally occurring anti-reflective
coating has proved exceedingly difficult. For example, top-down
manufacturing of GRIN, "moth-eye" structures have been demonstrated
with only limited efficacy, largely because standard lithography
processes either lack the necessary resolution or are ill-suited
for creating vertically tailored structures. Holographic
lithography has proven more versatile at creating GRIN structures,
but these techniques are expensive and still limited in their
resolution, which decreases the bandwidth of the anti-reflective
coatings.
[0011] A second approach to fabricating GRIN nanostructures is by
growth methods. For example, porous nanowire films, porous glass
films, and porous polymer films can be prepared by depositing a
binary mixture and subsequently removing one component. However,
the formation of a film with varying porosity has proven difficult
to control, while the formation of multi-layer structures with
decreasing porosity typically suffers from collapse due to high
porosity and low mechanical integrity of the outer layer(s) of the
film.
BRIEF SUMMARY OF THE INVENTION
[0012] What is needed is a method to deposit films having a tunable
refractive index gradient, and a transparent coating material that
can be manufactured using a straightforward manufacturing method
that has improved durability and anti-reflective properties.
[0013] The present invention provides surfaces resistant to the
reflection of electromagnetic radiation therefrom. These
anti-reflective surfaces can be used in traditional electronic
devices, as well as in industrial building and architectural
applications, health care applications, and the military and
decorative arts. The anti-reflective coatings of the present
invention can be prepared efficiently utilizing a low-cost
fabrication process.
[0014] The present invention is directed to a composition,
comprising: a substrate including a surface, and a multi-layer
coating of nanowires positioned on at least a portion of the
surface, the coating comprising three or more laminar layers of
nanowires, including a bottom layer of nanowires affixed to the
surface, and a top-most layer of nanowires, wherein a nanowire
within a laminar layer is oriented substantially parallel to
another nanowire within the same laminar layer, nanowires within
adjacent laminar layers are not substantially parallel to one
another, the top-most layer of nanowires has a refractive index of
about 5% to about 70% of a refractive index of the bottom layer of
nanowires, and the refractive index of the three or more laminar
layers of nanowires decreases by about 10% or more per laminar
layer from the bottom layer of nanowires to the top-most layer of
nanowires.
[0015] In some embodiments, a bottom layer of nanowires has a
refractive index of about 30% to about 100% of a refractive index
of the substrate, a top-most layer of nanowires has a refractive
index of about 1% to about 40% of the refractive index of the
substrate, and the refractive index of the three or more laminar
layers decreases by about 15% or more per layer from the bottom
layer of nanowires to the top-most layer of nanowires.
[0016] In some embodiments, the refractive index of the three or
more laminar layers of nanowires decreases alinearly from the
bottom layer of nanowires to the top-most layer of nanowires.
[0017] In some embodiments, the refractive index of the three or
more laminar layers of nanowires decreases linearly from the bottom
layer of nanowires to the top-most layer of nanowires.
[0018] In some embodiments, a thickness of a laminar layer within
the multi-layer coating of nanowires is approximately the diameter
of a nanowire present within the laminar layer.
[0019] In some embodiments, nanowires within adjacent laminar
layers of the multi-layer coating are substantially orthogonal to
one another.
[0020] In some embodiments, adjacent nanowires within a laminar
layer are spaced about evenly apart relative to one another, and
wherein a spacing separating adjacent nanowires within a laminar
layer is about 30% or less than an average length of the
nanowires.
[0021] In some embodiments, the nanowires have an average length of
about 200 nm to about 5 mm and an average diameter of about 1 nm to
about 10 .mu.m, or the nanowires have an average length of about
200 nm to about 5 mm and an average diameter of about 5 nm to about
1 .mu.m.
[0022] In some embodiments, the nanowires of at least the bottom
layer of the multi-layer coating have substantially the same
composition as the substrate.
[0023] In some embodiments, all of the nanowires present within the
multi-layer coating have approximately the same composition.
[0024] In some embodiments, the nanowires within the multi-layer
coating are not functionalized or derivatized.
[0025] In some embodiments, a coating further comprises a molecular
or polymeric matrix surrounding the multi-layer coating of
nanowires, wherein at least a portion of the top-most layer of
nanowires is exposed.
[0026] In some embodiments, a portion of the surface having the
anti-reflective multi-layer coating of nanowires thereon reflects
about 50% or less of an electromagnetic radiation having at least
one wavelength of about 180 nm to about 30 .mu.m compared to an
uncoated portion of the surface.
[0027] In some embodiments, a portion of the substrate having the
multi-layer coating of nanowires thereon has a resistance to crack
propagation that is about 3 times or more than a portion of the
substrate surface that lacks the multi-layer coating of
nanowires.
[0028] The present invention is also directed to a composition,
comprising: a metallic substrate including a surface, and an
anti-reflective multi-layer mat of nanowires positioned on at least
a portion of the surface, the multi-layer mat comprising three or
more laminar layers of nanowires and including a bottom layer of
nanowires affixed to the surface and a top-most layer of metallic
nanowires, wherein the top-most layer of nanowires has a refractive
index of about 5% to about 70% of a refractive index of the bottom
layer of nanowires, and wherein the refractive index of the three
or more laminar layers decreases by about 10% or more per layer
from the bottom layer of nanowires to the top-most layer of
nanowires.
[0029] In some embodiments, the substrate and the metallic
nanowires comprise at least one metal that can be the same or
different selected from: a transition metal, a Group 13 metal, a
Group 14 metal, a Group 15 metal, an oxide thereof, or a
combination thereof.
[0030] In some embodiments, a thickness of a laminar layer within
the mat of metallic nanowires is about ten times or less an average
diameter of a nanowire present within the laminar layer.
[0031] In some embodiments, the metallic nanowires within the
multi-layer mat are bound to the substrate and each other via
metal-metal bonds.
[0032] In some embodiments, a portion of the metallic substrate
having the multi-layer mat of nanowires thereon has a resistance to
crack propagation that is about 3 times or more than a portion of
the metallic substrate surface that lacks the multi-layer mat of
nanowires.
[0033] In some embodiments, the substrate having a multilayer mat
or coating of nanowires thereon has a retro-reflectance at 633 nm
that is at least 50% less than a retro-reflectance at 633 nm from
an uncoated substrate that lacks the multilayer coating of
nanowires. In some embodiments, the substrate having the multilayer
mat or coating of nanowires thereon has a retro-reflectance at one
or more wavelengths from about 400 nm to about 12 .mu.m that is at
least 50% less than a retro-reflectance from an uncoated substrate
that lacks the multilayer mat of nanowires at the same one or more
wavelengths.
[0034] The present invention is also directed to a composition,
comprising: a substrate including a surface, and anti-reflective
multi-layer coating positioned on at least a portion of the
surface, the coating comprising three or more laminar layers, each
layer comprising a matrix incorporating a different degree of
porosity compared to the other layers in the coating, wherein a
bottom layer of the coating is affixed to the surface, wherein the
bottom layer has a refractive index of about 60% to about 100% of a
refractive index of the substrate, wherein a top-most layer of the
coating has a refractive index of about 1% to about 40% of the
refractive index of the substrate, and wherein the refractive index
of the three or more laminar layers decreases by about 10% or more
per layer from the bottom layer of the coating to the top-most
layer of the coating.
[0035] In some embodiments, a portion of the surface having the
anti-reflective multi-layer coating thereon reflects about 50% or
less of an electromagnetic radiation having at least one wavelength
of about 180 nm to about 30 .mu.m compared to an uncoated portion
of the surface.
[0036] In some embodiments, the anti-reflective multi-layer coating
comprises a multitude of pores having a diameter of about 1 nm to
about 100 nm.
[0037] In some embodiments, the matrix comprises one or more
polymers selected from: a polystyrene, a polysiloxane, a
polyacrylate, a polyvinylpyrrolidone, a polycarbonate, a
polyalkyleneglycol, a substituted variant thereof, or a combination
thereof.
[0038] The present invention is also directed to a device,
comprising: a substrate including a surface; and an anti-reflective
multi-layer coating of nanowires positioned on the surface, the
coating comprising three or more laminar layers of nanowires and
including a bottom layer of nanowires affixed to the surface,
wherein a nanowire within a laminar layer is oriented substantially
parallel to another nanowire within the same laminar layer; wherein
nanowires within different laminar layers are not parallel to one
another; and the bottom layer of nanowires has a refractive index
of about 30% or more than a refractive index of a top-most layer of
nanowires.
[0039] In some embodiments, the device is chosen from: a display
device, an optical device, a solar cell, a sensor, a cellular
device, an avionic device, a nautical device, a projectile device,
and combinations thereof.
[0040] The present invention is also directed to a process for
preparing an anti-reflective multi-layer nanowire coating on at
least a portion of a surface of a substrate, the process
comprising:
[0041] disposing on the surface a first laminar layer of nanowires,
wherein the first laminar layer has a refractive index about 60% to
about 100% of a refractive index of the substrate;
[0042] affixing the first laminar layer of nanowires to the
surface;
[0043] disposing a second laminar layer of nanowires onto the first
laminar layer of nanowires;
[0044] affixing the second laminar layer of nanowires to the first
laminar layer of nanowires;
[0045] disposing at least a third laminar layer of nanowires onto
the second laminar layer of nanowires; and
[0046] affixing the third laminar layer of nanowires to the second
laminar layer of nanowires; wherein the second laminar layer of
nanowires has a refractive index less than the refractive index of
the first laminar layer of nanowires, and wherein the third laminar
layer of nanowires has a refractive index less than the refractive
index of the second laminar layer of nanowires.
[0047] In some embodiments, the process further comprises
activating the surface.
[0048] In some embodiments, the process further comprises:
[0049] aligning the nanowires within the first laminar layer to
orient the nanowires substantially parallel to one another;
[0050] aligning the nanowires within the second laminar layer to
orient the nanowires within the second laminar layer substantially
parallel to one another, wherein the nanowires within the second
laminar layer are not parallel to the nanowires within the first
laminar layer; and [0051] aligning the nanowires within the third
laminar layer to orient the nanowires within the third laminar
layer substantially parallel to one another, wherein the nanowires
within the third laminar layer are not parallel to the nanowires
within the second laminar layer.
[0052] In some embodiments, the process further comprises disposing
a fourth laminar layer of nanowires onto the third laminar layer of
nanowires, wherein the fourth laminar layer of nanowires has a
refractive index less than the refractive index of the third
laminar layer of nanowires.
[0053] In some embodiments, the process further comprises aligning
the nanowires within the fourth laminar layer to orient the
nanowires within the fourth laminar layer substantially parallel to
one another, wherein the nanowires within the fourth laminar layer
are not parallel to the nanowires within the third laminar
layer
[0054] In some embodiments, the aligning comprises at least one of:
applying a mechanical force to the nanowires, applying a magnetic
field to the nanowires, applying an electric field to the
nanowires, applying a fluid gradient to the nanowires, and
combinations thereof.
[0055] In some embodiments, the affixing comprises at least one of:
sintering, covalently bonding, cross-linking, melting, calcining,
encapsulating in a polymeric or molecular matrix, or a combination
thereof.
[0056] The present invention is also directed to a process for
preparing an anti-reflective multi-layer coating on at least a
portion of a surface of a substrate, the process comprising:
[0057] printing on the surface a first laminar layer comprising a
first polymer and an optional second polymer;
[0058] printing on the first laminar layer a second laminar layer
comprising the first polymer and the second polymer, wherein the
second laminar layer is substantially free from solvent, and the
second polymer is present in the second layer in a higher
concentration than the first layer;
[0059] printing on the second laminar layer a third laminar layer
comprising the first polymer and the second polymer, wherein the
third laminar layer is substantially free from solvent, and the
second polymer is present in the third layer in a higher
concentration than the second layer;
[0060] optionally exposing the first laminar layer to conditions
suitable for removing the second polymer from the first laminar
layer while retaining the first polymer within the first laminar
layer;
[0061] exposing the second laminar layer to conditions suitable for
removing the second polymer from the second laminar layer while
retaining the first polymer within the second laminar layer; and
[0062] exposing the third laminar layer to conditions suitable for
removing the second polymer from the third laminar layer while
retaining the first polymer within the third laminar layer to
provide an anti-reflective multi-layer coating having a refractive
index gradient.
[0063] In some embodiments, the optionally exposing is performed
simultaneous with the exposing the second laminar layer and the
exposing the third laminar layer.
[0064] In some embodiments, the optionally exposing is performed
prior to the printing on the first laminar layer a second laminar
layer; and the exposing the second laminar layer is performed prior
to printing on the second laminar layer a third laminar layer.
[0065] In some embodiments, the exposing comprises a process
selected from: heating the laminar layer, irradiating the laminar
layer with electromagnetic radiation, irradiating the laminar layer
with an electron beam, exposing to a selective solvent,
pyrrolizing, exposing the laminar layer to a plasma, and
combinations thereof.
[0066] In some embodiments, the printing comprises:
[0067] coating an elastomeric stamp with a composition comprising a
pre-determined amount of the first polymer, the optional second
polymer, and a solvent to provide a coated stamp;
[0068] phase separating the polymers on the coated stamp;
[0069] removing the solvent from the composition; and
[0070] contacting the coated stamp with the surface under
conditions sufficient to transfer the composition from the coated
stamp to the surface.
[0071] The present invention is also directed to a product prepared
by the above processes. Non-limiting examples of products include
an antenna, a mirror, a window, a watch glass, a dome, a cone, a
lens, and combinations thereof.
[0072] In some embodiments, the processes of the present invention
separate the growth and/or formation of a nanostructure from the
deposition procedure. Thus, a wide variety of nanowires,
nanoparticles, or binary films thereof can be utilized.
[0073] Further embodiments, features, and advantages of the present
inventions, as well as the structure and operation of the various
embodiments of the present invention, are described in detail below
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0074] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate one or more
embodiments of the present invention and, together with the
description, further serve to explain the principles of the
invention and to enable a person skilled in the pertinent art to
make and use the invention.
[0075] FIGS. 1A-1C provide a graphical representation of refractive
index versus coating depth or thickness for an ideal laminar
gradient refractive index coating, and laminar gradient refractive
index coatings of the present invention.
[0076] FIG. 2 provides a schematic cross-sectional representation
of an anti-reflective surface of the present invention.
[0077] FIGS. 3A and 3B provide three-dimensional schematic
representations of stamp structures suitable for use with the
present invention.
[0078] FIGS. 4A-4F provide a three-dimensional schematic
cross-sectional representation of a process for providing an
anti-reflective surface of the present invention.
[0079] FIGS. 5 and 6 provide optical microscopy images of
multi-layer nanowire coatings prepared by a process of the present
invention.
[0080] FIGS. 7A-7B provide a top-view schematic diagram of a
process for disposing multi-layer aligned nanowire coatings
directly to a substrate.
[0081] FIG. 8 provides a comparison of the anti-glare properties of
a coated substrate of the present invention with an uncoated
substrate.
[0082] FIGS. 9A-9F provide optical microscope images of uncoated
ZnS substrates and ZnS substrates comprising aligned ZrO.sub.2
nanowire coatings according to the present invention after being
subjected to water-jet impact durability testing.
[0083] FIG. 10 provides a schematic representation of an
experimental apparatus suitable for measuring the retro-reflectance
of the coated substrates of the present invention.
[0084] FIG. 11 provides a cross-sectional schematic representation
of a deposition apparatus suitable for disposing aligned nanowires
on a curved substrate via electrospinning.
[0085] One or more embodiments of the present invention will now be
described with reference to the accompanying drawings. In the
drawings, like reference numbers can indicate identical or
functionally similar elements. Additionally, the left-most digit(s)
of a reference number can identify the drawing in which the
reference number first appears.
DETAILED DESCRIPTION OF THE INVENTION
[0086] This specification discloses one or more embodiments that
incorporate the features of this invention. The disclosed
embodiment(s) merely exemplify the invention. The scope of the
invention is not limited to the disclosed embodiment(s). The
invention is defined by the claims appended hereto.
[0087] The embodiment(s) described, and references in the
specification to "one embodiment," "an embodiment," "an example
embodiment," etc., indicate that the embodiment(s) described can
include a particular feature, structure, or characteristic, but
every embodiment may not necessarily include the particular
feature, structure, or characteristic. Moreover, such phrases are
not necessarily referring to the same embodiment. Further, when a
particular feature, structure, or characteristic is described in
connection with an embodiment, it is understood that it is within
the knowledge of one skilled in the art to effect such feature,
structure, or characteristic in connection with other embodiments
whether or not explicitly described.
[0088] References to spatial descriptions (e.g., "above," "below,"
"up," "down," "top," "bottom," etc.) made herein are for purposes
of description and illustration only, and should be interpreted as
non-limiting upon the stamps, substrates, coatings, methods, and
products of any method of the present invention, which can be
spatially arranged in any orientation or manner.
Nanowires
[0089] The present invention refers to nanowire coatings, methods
to prepare the coatings, and products prepared therefrom. As used
herein, a "nanowire" refers to an elongated conductive or
semiconductive material (or other material described herein) that
includes at least one cross sectional dimension of about 500 nm of
less, about 100 nm or less, or about 50 nm or less, and has an
aspect ratio (length:width) of about 10 or more, about 50 or more,
about 100 or more, or about 1,000 or more. As used herein, the term
"nanowire" is interchangeable with the terms "nanorod," "nanotube,"
"nanoribbon," "nanofiber," and the like, and combinations thereof.
Thus, nanowires for use with the present invention are not limited
to objects having a tubular or cylindrical shape, but can also
include tubes and/or cylinders having a circular, ellipsoidal or
irregular cross section, as well as cones, rods, ribbons, and the
like.
[0090] As used herein, the term "nanotube" refers to a cylindrical
structure having a hollow, filled, or partially filled
tube-portion. Thus, as used herein, "nanowires" can include carbon
nanotubes and nanotubes comprising conductive and/or semiconductive
organic and/or inorganic materials.
[0091] As used herein, the term "nanoribbon" refers to a flat,
laminar, curled, spiral and/or elongated structure comprising at
least one of an insulating material, a semiconductive material, a
conductive material, or a combination thereof.
[0092] As used herein, the term "nanorod" refers to any elongated
conductive or semiconductive material (or other material described
herein) similar to a nanowire, but having an aspect ratio
(length:width) less than that of a nanowire.
[0093] As used herein, the term "nanofiber" refers to an elongated
conductive or semiconductive material (or other material described
herein) similar to a nanowire, but having an aspect ration
(length:width) greater than that of a nanowire. In some
embodiments, a nanofiber has a length of about 1 mm to about 1 m,
about 1 mm to about 500 mm, about 1 mm to about 100 mm, about 1 mm
to about 50 mm, or about 1 mm to about 10 mm.
[0094] As used herein, an "aspect ratio" is the length of a first
axis of a nanostructure divided by the average of the lengths of
the second and third axes of the nanostructure, where the second
and third axes are the two axes whose lengths are most nearly equal
to each other. For example, the aspect ratio for a perfect rod
would be the length of its long axis divided by the diameter of a
cross-section perpendicular to (normal to) the long axis.
[0095] In some embodiments, a nanowire is porous. As used herein,
"porous" and "porosity" are interchangeable and refer to a
structure comprising void space. Nanowires for use with the present
invention can have a porosity of about 1% to about 65% by volume,
about 5% to about 60% by volume, about 10% to about 50% by volume,
about 15% to about 40% by volume, or about 20% to about 30% by
volume.
[0096] In some embodiments, the nanowires have an average length of
about 200 nm to about 1 m, about 200 nm to about 500 mm, about 200
nm to about 100 mm, about 200 nm to about 10 mm, about 200 nm to
about 1 mm, about 200 nm to about 200 .mu.m, about 200 nm to about
50 .mu.m, about 200 nm to about 10 .mu.m, about 500 nm to about 50
mm, about 500 nm to about 10 mm, about 500 nm to about 1 mm, about
500 nm to about 500 .mu.m, about 500 nm to about 50 .mu.m, about
500 nm to about 10 .mu.m, about 1 .mu.m to about 100 mm, about 1
.mu.m to about 10 mm, about 1 .mu.m to about 1 mm, about 1 .mu.m to
about 500 .mu.m, or about 1 .mu.m to about 100 .mu.m.
[0097] In some embodiments, the nanowires have an average diameter
of about 5 nm to about 20 .mu.m, about 5 nm to about 10 .mu.m,
about 5 nm to about 1 .mu.m, about 5 nm to about 500 nm, about 5 nm
to about 250 nm, about 5 nm to about 100 nm, about 5 nm to about 75
nm, about 5 nm to about 50 nm, about 5 nm to about 25 nm, about 10
nm to about 10 .mu.m, about 10 nm to about 1 .mu.m, about 10 nm to
about 750 nm, about 10 nm to about 500 nm, about 10 nm to about 250
nm, about 10 nm to about 100 nm, about 10 nm to about 75 nm, about
10 nm to about 50 nm, about 25 nm to about 10 .mu.m, about 25 nm to
about 1 .mu.m, about 25 nm to about 750 nm, about 25 nm to about
500 nm, about 25 nm to about 250 nm, about 25 nm to about 100 nm,
about 50 nm to about 10 .mu.m, about 50 nm to about 1 .mu.m, about
50 nm to about 750 nm, about 50 nm to about 500 nm, about 50 nm to
about 250 nm, about 50 nm to about 100 nm, about 100 nm to about 10
.mu.m, about 100 nm to about 1 .mu.m, about 100 nm to about 750 nm,
about 100 nm to about 500 nm, about 100 nm to about 250 nm, about
500 nm to about 10 .mu.m, about 500 nm to about 1 .mu.m, or about
500 nm to about 750 nm.
[0098] In some embodiments, a deposited array of nanowires
comprises nanowires having an average diameter of about 100 nm to
about 5 .mu.m, about 500 nm to about 5 .mu.m, or about 1 .mu.m to
about 5 .mu.m. The deposited array of nanowires can be optionally
annealed, calcined, or otherwise post-treated to provide an array
of nanowires comprising nanowires having an average diameter of
about 50 nm to about 500 nm, about 100 nm to about 500 nm, or about
300 nm to about 500 nm.
[0099] The diameter (e.g., thickness and/or width) of nanowires can
be varied to provide enhanced anti-reflection for different
wavelengths or ranges of wavelengths in the electromagnetic
spectrum. Not being bound by any particular theory, for a
wavelength range, .lamda..sub.1-.lamda..sub.2, wherein
.lamda..sub.1 is the lowest wavelength of radiation for which
anti-reflection is sought and .lamda..sub.2 is the longest
wavelength of radiation for which anti-reflection is sought, the
diameter of a nanowire within a coating of the present invention
can be about 0.10(.lamda..sub.1) to about 0.25(.lamda..sub.1), and
the total thickness of the multi-layer coating can be about
0.25(.lamda..sub.2) or more.
[0100] Nanowires for use with the present invention can be rigid or
flexible. In some embodiments, a nanowire can undergo plastic
deformation such that conformal contact can be made between a
flexible nanowire and a curved or non-planar substrate.
[0101] In some embodiments, a nanowire for use with the present
invention comprises a metal selected from: gold, nickel, palladium,
iridium, cobalt, chromium, aluminum, titanium, tin, and the like,
an alloy thereof, a polymer, a conductive polymer, a ceramic, a
composite thereof, and combinations thereof. Other presently known
and later developed conductive or semiconductive materials can also
be employed.
[0102] In some embodiments, a nanowire for use with the present
invention comprises a material selected from: an aluminum oxide
(e.g., Al.sub.2O.sub.3), a zirconium oxide (e.g., ZrO.sub.2), a
titanium oxide (e.g., TiO.sub.2), a yttrium oxide (e.g.,
Y.sub.2O.sub.3), a zinc oxide (e.g., ZnO), a zinc sulfide (e.g.,
ZnS), a germanium oxide, (e.g., GeO, GeO.sub.2, and the like),
copper oxide (e.g., Cu.sub.2O, and the like), silver oxide (e.g.,
AgO), carbon, an indium tin oxide, a suboxide thereof, and
combinations thereof.
[0103] In some embodiments, a nanowire suitable for use with the
present invention is a ZrO.sub.2 nanowire having a mean diameter of
about 150 nm to about 600 nm. In some embodiments, a nanowire
suitable for use with the present invention is a GeO nanowire
having a mean diameter of about 50 nm to about 200 nm. In some
embodiments, a nanowire suitable for use with the present invention
is a TiO.sub.2 nanowire having a mean diameter of about 50 nm to
about 200 nm. In some embodiments, a nanowire suitable for use with
the present invention is a ZnO nanowire having a mean diameter of
about 50 nm to about 500 nm.
[0104] In some embodiments, the nanowires of at least the bottom
layer of the coating have substantially the same composition of the
substrate.
[0105] In some embodiments, a nanowire absorbs electromagnetic
radiation having at least one wavelength of about 180 nm to about
30 .mu.m. Thus, in some embodiments a coating of the present
invention does not substantially reflect or transmit at least one
wavelength of about 180 nm to about 30 .mu.m. In some embodiments,
a nanowire is substantially transparent to electromagnetic
radiation having at least one wavelength of about 180 nm to about
30 .mu.m. Thus, in some embodiments a coating of the present
invention effectively transmits at least one wavelength of about
180 nm to about 30 .mu.m.
[0106] In some embodiments, all of the nanowires present within a
multi-layer coating have approximately the same composition. In
some embodiments, all of the nanowires present within a laminar
layer of a coating of the present invention have substantially the
same composition. In some embodiments, nanowires in different
layers of a coating of the present invention have compositions that
differ from one another, or that differ substantially from one
another.
[0107] In some embodiments, the nanowires within a multi-layer
coating of the present invention are not functionalized and/or
derivatized. In some embodiments, nanowires with a coating of the
present invention are functionalized and/or derivatized. As used
herein, "functionalized" and "derivatized" refer to the attachment
of a chemical group, ligand, species, moiety, and the like to a
nanowire, coating layer, or surface of a coating of the present
invention. In some embodiments, nanowires, layers and/or coatings
are derivatized with a molecular species as described herein, or an
oligomer, a dendrimer, a polymer, a nanoparticle, or a metal
complex thereof, wherein a molecular species is present as a repeat
unit in an oligomer, dendrimer, polymer, or nanoparticle, or as a
ligand in a metal complex.
[0108] Not being bound by any particular theory, functionalization
and derivatization can be achieved via a covalent bonding
interaction, an ionic bonding interaction, a hydrogen bonding
interaction, a non-bonding interaction, an intercalation
interaction, physical entanglement, a chiral interaction, a
magnetic interaction, and combinations thereof. Derivatization and
functionalization can be performed to increase an adhesive
interaction with a substrate, increase the solubility of nanowires
in a solvent, increase the hydrophobicity of a coating, increase
the hydrophilicity of a coating, and combinations thereof.
[0109] A molecular species, oligomer, dendrimer, polymer,
nanoparticle, and metal complex suitable for use with the present
invention can be functionalized with one of the following groups to
facilitate an association with a substrate: hydroxyl, alkoxyl,
thiol, alkylthio, silyl, alkylsilyl, alkylsilenyl, siloxyl, primary
amino, secondary amino, tertiary amino, carbonyl, alkylcarbonyl,
aminocarbonyl, carbonylamino, carboxy, and combinations
thereof.
[0110] In some embodiments, the nanowires and/or coatings are
hydrophobic. In some embodiments, a nanowire or coating can be
derivatized with a hydrophobic functional group. As used herein,
"hydrophobic" refers to coatings that have a tendency to repel
water, are resistant to water and/or cannot be wetted by water. For
example, in some embodiments water deposited on a hydrophobic
coating of the present invention forms a droplet having a contact
angle of about 90.degree. to about 180.degree.. In some
embodiments, water deposited onto a hydrophobic coating of the
present invention forms a minimum contact angle of about
90.degree., about 100.degree., about 110.degree., about
120.degree., about 130.degree., about 140.degree., about
150.degree., or about 160.degree..
[0111] In some embodiments, a hydrophobic molecular species
comprises an optionally substituted C.sub.1-C.sub.60 alkyl, an
optionally substituted C.sub.2-C.sub.60 alkenyl, an optionally
substituted C.sub.2-C.sub.60 alkynyl, an optionally substituted
C.sub.6-C.sub.60 aryl, an optionally substituted C.sub.6-C.sub.60
aralkyl, an optionally substituted C.sub.6-C.sub.60 heteroaryl, and
combinations thereof, wherein these groups can be linear or
branched. Optional substituents for hydrophobic molecular species
include, but are not limited to, a halo and perhalo (i.e., wherein
halo is any one of: fluorine, chlorine, bromine, iodine, and
combinations thereof), alkylsilyl, siloxyl, tertiary amino, and
combinations thereof.
[0112] In some embodiments, an optionally substituted hydrophobic
molecular species is chosen from a C.sub.1-C.sub.60 fluoroalkyl, a
C.sub.1-C.sub.60 perfluoroalkyl, and combinations thereof.
[0113] Functional groups suitable for imparting hydrophilicity to a
nanowire and/or coating of the present invention include, but are
not limited to, hydroxyl, alkoxyl, thiol, thioalkyl, silyl,
alkylsilyl, alkylsilenyl, siloxyl, primary amino, secondary amino,
tertiary amino, carbonyl, alkylcarbonyl, aminocarbonyl,
carbonylamino, carboxy, alkylenedioxy, and combinations thereof.
Not being bound by any particular theory, alkylsilyl, alkylsilenyl,
siloxyl, primary amino, secondary amino, tertiary amino,
alkylcarbonyl, aminocarbonyl, carbonylamino, and carboxy functional
groups can also impart hydrophobicity to a surface depending on the
presence and length of an --R group attached to the functional
group, wherein R is, e.g., alkyl, alkenyl, alkynyl, and the like,
wherein increasing the number of carbon atoms present in R
increases the hydrophobicity of a coating layer.
[0114] As used herein, "alkyl," by itself or as part of another
group, refers to straight and branched chain hydrocarbons of up to
60 carbon atoms, such as, but not limited to, octyl, decyl,
dodecyl, hexadecyl, and octadecyl.
[0115] As used herein, "alkenyl," by itself or as part of another
group, refers to a straight and branched chain hydrocarbons of up
to 60 carbon atoms, wherein there is at least one double bond
between two of the carbon atoms in the chain, and wherein the
double bond can be in either of the cis or trans configurations,
including, but not limited to, 2-octenyl, 1-dodecenyl,
1-8-hexadecenyl, 8-hexadecenyl, and 1-octadecenyl.
[0116] As used herein, "alkynyl," by itself or as part of another
group, refers to straight and branched chain hydrocarbons of up to
60 carbon atoms, wherein there is at least one triple bond between
two of the carbon atoms in the chain, including, but not limited
to, 1-octynyl and 2-dodecynyl.
[0117] As used herein, "aryl," by itself or as part of another
group, refers to cyclic, fused cyclic, and multi-cyclic aromatic
hydrocarbons containing up to 60 carbons in the ring portion.
Typical examples include phenyl, naphthyl, anthracenyl, fluorenyl,
tetracenyl, pentacenyl, hexacenyl, perylenyl, terylenyl,
quaterylenyl, coronenyl, fullerenyl and buckminsterfullerenyl.
[0118] As used herein, "aralkyl" or "arylalkyl," by itself or as
part of another group, refers to alkyl groups as defined above
having at least one aryl substituent, such as benzyl, phenylethyl,
and 2-naphthylmethyl. Similarly, the term "alkylaryl," as used
herein by itself or as part of another group, refers to an aryl
group, as defined above, having an alkyl substituent, as defined
above.
[0119] As used herein, "heteroaryl," by itself or as part of
another group, refers to cyclic, fused cyclic and multicyclic
aromatic groups containing up to 30 atoms in the ring portions,
wherein the atoms in the ring(s), in addition to carbon, include at
least one heteroatom. The term "heteroatom" is used herein to mean
an oxygen atom ("O"), a sulfur atom ("S") or a nitrogen atom ("N").
Additionally, the term heteroaryl also includes N-oxides of
heteroaryl species that containing a nitrogen atom in the ring.
Typical examples include pyrrolyl, pyridyl, pyridyl N-oxide,
thiophenyl, and furanyl.
[0120] Any one of the above groups can be further substituted with
at least one of the following substituents: hydroxyl, alkoxyl,
thiol, alkylthio, silyl, alkylsilyl, alkylsilenyl, siloxyl, primary
amino, secondary amino, tertiary amino, carbonyl, alkylcarbonyl,
aminocarbonyl, carbonylamino, carboxy, halo, perhalo,
alkylenedioxy, and combinations thereof.
[0121] As used herein, "hydroxyl," by itself or as part of another
group, refers to an (--OH) moiety.
[0122] As used herein, "alkoxyl," by itself or as part of another
group, refers to one or more alkoxyl (--OR) moieties, wherein R is
selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and
heteroaryl groups described above.
[0123] As used herein, "thiol," by itself or as part of another
group, refers to an (--SH) moiety.
[0124] As used herein, "alkylthio," refers to an (--SR) moieties,
wherein R is selected from the alkyl, alkenyl, alkynyl, aryl,
aralkyl, and heteroaryl groups described above.
[0125] As used herein, "silyl," by itself or as part of another
group, refers to an (--SiH.sub.3) moiety.
[0126] As used herein, "alkylsilyl," by itself or as part of
another group, refers to an (--Si(R).sub.xH.sub.y) moiety, wherein
1.ltoreq.x.ltoreq.3 and y=3-x, and wherein R is independently
selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and
heteroaryl groups described above.
[0127] As used herein, "alkylsilenyl," by itself or as part of
another group, refers to a (--Si(.dbd.R)H) moiety, wherein R is
selected from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and
heteroaryl groups described above.
[0128] As used herein, "siloxyl," by itself or as part of another
group, refers to a (--Si(OR).sub.xR.sup.1.sub.y) moiety, wherein
1.ltoreq.x.ltoreq.3 and y=3-x, wherein R and R.sup.1 are
independently selected from hydrogen and the alkyl, alkenyl,
alkynyl, aryl, aralkyl, and heteroaryl groups described above.
[0129] As used herein, "primary amino," by itself or as part of
another group, refers to an (--NH.sub.2) moiety.
[0130] As used herein, "secondary amino," by itself or as part of
another group, refers to an (--NRH) moiety, wherein R is selected
from the alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl
groups described above.
[0131] As used herein, "tertiary amino," by itself or as part of
another group, refers to an (--NRR.sup.1) moiety, wherein R and
R.sup.1 are independently selected from the alkyl, alkenyl,
alkynyl, aryl, aralkyl, and heteroaryl groups described above.
[0132] As used herein, "carbonyl," by itself or as part of another
group, refers to a (C.dbd.O) moiety.
[0133] As used herein, "alkylcarbonyl," by itself or as part of
another group, refers to a (--C(.dbd.O)R) moiety, wherein R is
independently selected from hydrogen and the alkyl, alkenyl,
alkynyl, aryl, aralkyl, and heteroaryl groups described above.
[0134] As used herein, "aminocarbonyl," by itself or as part of
another group, refers to a (--C(.dbd.O)NRR.sup.1) moiety, wherein R
and R.sup.1 are independently selected from hydrogen and the alkyl,
alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups described
above.
[0135] As used herein, "carbonylamino," by itself or as part of
another group, refers to a (--N(R)C(.dbd.O)R.sup.1) moiety, wherein
R and R.sup.1 are independently selected from hydrogen and the
alkyl, alkenyl, alkynyl, aryl, aralkyl, and heteroaryl groups
described above.
[0136] As used herein, "carboxy," by itself or as part of another
group, refers to a (--COOR) moiety, wherein R is independently
selected from hydrogen and the alkyl, alkenyl, alkynyl, aryl,
aralkyl, and heteroaryl groups described above.
[0137] As used herein, "alkylenedioxy," by itself or as part of
another group, refers to a ring and is especially C.sub.1-4
alkylenedioxy. Alkylenedioxy groups can optionally be substituted
with halogen (especially fluorine). Typical examples include
methylenedioxy (--OCH.sub.2O--) or difluoromethylenedioxy
(--OCF.sub.2O--).
[0138] As used herein, "halo," by itself or as part of another
group, refers to any of the above alkyl, alkenyl, alkynyl, aryl,
aralkyl, and heteroaryl groups wherein one or more hydrogens
thereof are substituted by one or more fluorine, chlorine, bromine,
or iodine atoms.
[0139] As used herein, "perhalo," by itself or as part of another
group, refers to any of the above alkyl, alkenyl, alkynyl, aryl,
aralkyl, and heteroaryl groups wherein all of the hydrogens thereof
are substituted by fluorine, chlorine, bromine, or iodine
atoms.
[0140] In some embodiments, a nanowire coating or layer of the
present invention can be fluorinated after deposition with a
fluorine atom and/or a fluorinated moiety. As used herein, a
"fluorinated moiety" refers to a molecule, particulate, polymer,
oligomer, or precursor that contains a bond to fluorine and can be
used to derivatize a nanowire, a layer, and/or a coating of the
present invention. In some embodiments, a fluorinated moiety
comprises a C--F bond and/or an Si--F bond. For example, in some
embodiments, an outer surface of a multi-layer coating can be
fluorinated (e.g., by exposure to F.sub.2, SiF.sub.4, SF.sub.6, a
fluorinated alkyl and/or alkoxy silane, and the like, as well as
other fluorination processes that would be apparent to a person of
ordinary skill in the art of surface fluorination) to provide a
fluorinated surface. Alternatively, nanowires used to prepare a
coating of the present invention can be fluorinated prior to
formation of the coating such that fluorinated groups are present
throughout the coating.
[0141] Further nanowire compositions suitable for use with the
present invention are described in U.S. Patent Publication Nos.
2002/0094450 A1, 2002/0175408 A1, 2006/0019472 A1, 2007/0120095 A1,
and 2007/0281156 A1, each of which is incorporated herein by
reference in its entirety.
Substrates and Articles for Use with the Anti-Reflective
Coatings
[0142] The anti-reflective coatings of the present invention are
formed on a substrate or article. Substrates suitable for
patterning by the methods of the present invention are not
particularly limited by size, composition or geometry. For example,
the present invention is suitable for patterning planar,
multi-planar or tiered, non-planar, flat, curved, spherical, rigid,
flexible, symmetric, and asymmetric substrates, and any combination
thereof. The methods are also not limited by surface roughness or
surface waviness, and are equally applicable to smooth, rough and
wavy substrates, and substrates exhibiting heterogeneous surface
morphology (i.e., substrates having varying degrees of smoothness,
roughness and/or waviness).
[0143] As used herein, a substrate is "planar" if, after accounting
for random variations in the height of a substrate (e.g., surface
roughness, waviness, etc.), four points on the surface of the
substrate lie in approximately the same plane. Planar substrates
can include, but are not limited to, windows, embedded circuits,
laminar sheets, and the like. Planar substrates can include flat
variants of the above having holes there through.
[0144] As used herein, a substrate is "non-planar" if, after
accounting for random variations in the height of a substrate
(e.g., surface roughness, waviness, etc.), four or more points on
the surface of the substrate do not lie in the same plane.
Non-planar substrates can include, but are not limited to,
gratings, substrates comprising multiple different planar areas
(i.e., "multi-planar" substrates), substrates having a tiered
geometry, and combinations thereof. Non-planar substrates can
comprise flat and/or curved areas.
[0145] As used herein, a substrate is "curved" when the radius of
curvature of a substrate is non-zero over a distance of 100 .mu.m
or more, or 1 mm or more, across the surface of a substrate.
[0146] As used herein, a substrate is "rigid" when the plane,
curvature, and/or geometry of a substrate cannot be easily
distorted. Rigid substrates can undergo temperature-induced
distortions due to thermal expansion, or become flexible at
temperatures above a glass transition, melting point, and the
like.
[0147] The plane, curvature, and/or geometry of a flexible
substrate can be distorted flexed, and/or undergo elastic or
plastic deformation, bending, compression, twisting, and the like
in response to applied external force, stress, strain and/or
torsion. Typically, a flexible substrate can be moved between flat
and curved geometries. Flexible substrates suitable for use with
the present invention include, but are not limited to, polymers
(e.g., plastics), woven fibers, thin films, metal foils, composites
thereof, laminates thereof, and combinations thereof. In some
embodiments, a flexible substrate can be patterned using the
methods of the present invention in a reel-to-reel manner.
[0148] Substrates for use with the present invention are not
particularly limited by composition. Substrates suitable for use
with the present invention include materials chosen from metals,
crystalline materials (e.g., monocrystalline, polycrystalline, and
partially crystalline materials), amorphous materials, conductors,
semiconductors, insulators, optics, painted substrates, fibers,
glasses, ceramics, zeolites, plastics, thermosetting and
thermoplastic materials (e.g., optionally doped: polyacrylates,
polycarbonates, polyurethanes, polystyrenes, cellulosic polymers,
polyolefins, polyamides, polyimides, resins, polyesters,
polyphenylenes, and the like), films, thin films, foils, plastics,
polymers, wood, fibers, minerals, biomaterials, living tissue,
bone, alloys thereof, composites thereof, laminates thereof, porous
variants thereof, doped variants thereof, and combinations
thereof.
[0149] In some embodiments, the substrates are transparent,
translucent, or opaque to visible, UV, and/or infrared light). In
some embodiments, a substrate is black, and an optically absorbing
nanowire coating of the present invention is applied thereto to
provide a "perfectly" black article or object. In some embodiments,
a substrate for use with the present invention is substantially
transparent in the wavelength range of about 450 nm to about 900
nm, or about 8 .mu.m to about 13 .mu.m.
[0150] In some embodiments, at least a portion of a substrate is
conductive or semiconductive. As used herein, "conductive" and
"semiconductive" materials include species, compounds, polymers,
films, coatings, substrates, and the like capable of transporting
or carrying electrical charge. Generally, the charge transport
properties of a semiconductive material can be modified based upon
an external stimulus such as, but not limited to, an electrical
field, a magnetic field, a temperature change, a pressure change,
exposure to radiation, and combinations thereof. In some
embodiments, a conductive or semiconductive material has an
electron or hole mobility of about 10.sup.-6 cm.sup.2/Vs or more,
about 10.sup.-5 cm.sup.2/Vs or more, about 10.sup.-4 cm.sup.2/Vs or
more, about 10.sup.-3 cm.sup.2/Vs or more, about 0.01 cm.sup.2/Vs
or more, or about 0.1 cm.sup.2/Vs or more. Electrically conductive
and semiconductive materials include, but are not limited to,
metals, alloys, thin films, crystalline materials, amorphous
materials, polymers, laminates, foils, plastics, and combinations
thereof.
[0151] In some embodiments, the substrate comprises a semiconductor
such as, but not limited to: crystalline silicon, polycrystalline
silicon, amorphous silicon, p-doped silicon, n-doped silicon,
silicon oxide, silicon germanium, germanium, gallium arsenide,
gallium arsenide phosphide, indium tin oxide, and combinations
thereof.
[0152] In some embodiments, the substrate comprises a glass such
as, but not limited to, undoped silica glass (SiO.sub.2),
fluorinated silica glass, borosilicate glass, borophosphorosilicate
glass, organosilicate glass, porous organosilicate glass, and
combinations thereof.
[0153] In some embodiments, the substrate comprises a ceramic such
as, but not limited to, zinc sulfide (ZnS.sub.x), boron phosphide
(BP.sub.x), gallium phosphide (GaP.sub.x), silicon carbide
(SiC.sub.x), hydrogenated silicon carbide (H:SiC.sub.x), silicon
nitride (SiN.sub.x), silicon carbonitride (SiC.sub.xN.sub.y),
silicon oxynitride (SiO.sub.xN.sub.y), silicon oxycarbide
(SiO.sub.xC.sub.y), silicon carbon-oxynitride
(SiC.sub.xO.sub.yN.sub.z), alumina (Al.sub.xO.sub.y), germania
(Ge.sub.xO.sub.y), hydrogenated variants thereof, doped variants
(e.g., n-doped and p-doped variants) thereof, and combinations
thereof (where x, y, and z can vary independently from about 0.1 to
about 5, about 0.1 to about 3, about 0.2 to about 2, or about 0.5
to about 1). In some embodiments, a ceramic substrate has a native
oxide and/or a deposited oxide layer thereon.
[0154] In some embodiments, the substrate comprises a metal such
as, but not limited to, germanium, copper, nickel, cobalt,
chromium, titanium, niobium, molybdenum, rhodium, palladium,
silver, cadmium, indium, tantalum, tungsten, iridium, platinum,
gold, and combinations thereof. In some embodiments, a metal
substrate has a native oxide and/or a deposited oxide layer
thereon.
[0155] In some embodiments, a substrate is selected from the group
consisting of: ZnS, silicon, sapphire, germanium, and combinations
thereof.
[0156] In some embodiments, the substrate comprises a flexible
material, such as, but not limited to: a plastic, a composite, a
laminate, a thin film, a metal foil, and combinations thereof.
[0157] The methods and structures of the present invention are
suitable for application in electrical systems, optical systems,
consumer electronics, industrial electronics, automobiles, military
applications, wireless systems, space applications, and any other
applications in which anti-reflective coatings are required or
desirable.
[0158] The present invention is also directed to articles, objects
and devices comprising the multi-layer coatings of the present
invention. Exemplary articles, objects and devices comprising the
substrates on which the anti-reflective and protective nanowire
coatings of the present invention can be applied include, but are
not limited to, windows; mirrors; radar domes (e.g., missile domes,
radar enclosures, and the like); communications devices; optical
elements (e.g, optical elements for use in eyeglasses, cameras,
binoculars, telescopes, night-vision goggles, range-finding sights,
IR viewers, and the like); lenses (e.g., fresnel lenses, etc.);
watch crystals; optical fibers, output couplers, input couplers,
microscope slides, holograms; cathode ray tube devices (e.g.,
computer and television screens); optical filters; data storage
devices (e.g., compact discs, DVD discs, CD-ROM discs, and the
like); flat panel electronic displays (e.g., LCDs, plasma displays,
and the like); touch-screen displays (such as those of computer
touch screens and personal data assistants); solar cells; flexible
electronic displays (e.g., electronic paper and books); cellular
phones; global positioning systems; calculators; graphic articles
(e.g., signage); motor vehicles (e.g., wind screens, windows,
displays, and the like); artwork (e.g., sculptures, paintings,
lithographs, and the like); membrane switches; jewelry; and
combinations thereof.
[0159] In some embodiments, the anti-reflective coatings of the
present invention can be used as an outer surface of a display or
optical device without applying an additional protective layer to
the coatings. For example, in some embodiments there is no
additional hard coating or anti-static coating applied to the
anti-reflective coating of the present invention.
[0160] The surface area of a substrate is not particularly limited
and can be easily scaled by the proper design of equipment suitable
for disposing the anti-reflective coatings of the present
invention, and can range, without limitation, from about 1 mm.sup.2
to about 20 m.sup.2, or about 1 cm.sup.2 to about 10 m.sup.2.
[0161] The substrates suitable for use with the present invention,
and the anti-reflective coatings provided thereon can be
structurally and compositionally characterized using analytical
methods known to those of ordinary skill in the art of thin film
fabrication and characterization.
Anti-Reflective Coatings
[0162] The present invention is directed to compositions comprising
a substrate including a surface and having on at least a portion of
the surface a multi-layer coating of nanowires comprising three or
more laminar layers of nanowires. The compositions include a bottom
layer of nanowires affixed to the surface, and a top-most layer of
nanowires, wherein nanowires present within a laminar layer are
oriented substantially parallel to each other, and nanowires within
adjacent laminar layers are not substantially parallel to each
other. In some embodiments, the top-most layer of nanowires has a
refractive index of about 5% to about 70% of a refractive index of
the bottom layer of nanowires, and the refractive index of the
three or more laminar layers of nanowires decreases by about 10% or
more per laminar layer from the bottom layer of nanowires to the
top-most layer of nanowires.
[0163] As used herein, a "coating" refers to a multi-layer film or
laminate on a substrate. The coatings of the present invention are
anti-reflective. In some embodiments, the coatings of the present
invention are also smudge-resistant.
[0164] As used herein, a "lattice" refers to a three dimensional
array of interlocking nanowires comprised by a coating of the
present invention. In some embodiments, a multi-layer coating of
the present invention forms a lattice of nanowires.
[0165] As used herein, "laminar layers" refers to a coating
comprised of layers that are substantially conformal or evenly coat
a substrate, wherein adjacent layers within the coating are adhered
to one another but do not substantially overlap.
[0166] The layers and coatings of the present invention can be
characterized based upon the refractive index. As used herein, a
"refractive index" of a layer refers to a volume average refractive
index. For example, for a layer comprising two components (e.g., a
nanowire having a refractive index, n>1.0, and air having a
refractive index, n=1.00293) the refractive index of the layer is
approximately the volume average of the first component of the
layer and the volume average of the second component of the layer
multiplied by the refractive index of the first and second
components, respectively. Thus, the refractive index of a layer
comprising multiple components can be approximated using equation
(1):
n.sub.LAYER=n.sub.1V.sub.1+n.sub.2V.sub.2 . . . +n.sub.xV.sub.x
(1)
where V.sub.1, V.sub.2 and V.sub.x are the average percentage
volumes of the first, second and xth components of the layer,
respectively, and wherein V.sub.1+V.sub.2 . . . +V.sub.x=100%
volume.
[0167] The anti-reflective coatings of the present invention have
an anisotropic refractive index in at least the vertical direction
(i.e., a non-homogeneous refractive index in at least the z-axis),
and can also exhibit anisotropy in a lateral direction of, e.g., a
layer of a coating.
[0168] Non-limiting examples of tools suitable for measuring a
refractive index of a coating or a layer of the present invention
include a refractometer, a gonioreflectometer, an ellipsometer, and
any other analytical tools known to a person of ordinary skill in
the art.
[0169] A refractive index of a layer and/or coating of the present
invention can be measured at any wavelength in the electromagnetic
spectrum from about 180 nm to about 30 .mu.m. In some embodiments,
a refractive index of a layer and/or coating is measured using the
sodium D-line (.lamda.=589.29 nm).
[0170] In some embodiments, the refractive index of a layer within
a coating can be determined based on the refractive index of
another layer within a coating. For example, in some embodiments a
top-most layer of nanowires in a coating has a refractive index of
about 5% to about 70% of a refractive index of a bottom layer of
nanowires. As used herein, a percentage of a refractive index can
be calculated using equation (2):
n.sub.LAYER2=[(n.sub.LAYER1-1.0).times.%]+1.0 (2)
where n.sub.LAYER2 is the refractive index of a second layer,
n.sub.LAYER1 is the refractive index of a first layer of a coating,
and "%" is the percentage change between the first and second
layers of the coating. Thus, given a first layer having a
refractive index, n.sub.LAYER1=3.0, a second layer having a
refractive index of about 5% to about 70% of the first layer would
have a refractive index of about n.sub.LAYER2=1.1 to about
n.sub.LAYER2=2.4.
[0171] The coatings of the present invention are affixed to a
substrate. As used herein, "affixed" refers to the coatings of the
present invention having an adhesive interaction with a substrate.
An adhesive interaction between the coatings and a substrate can be
a covalent bonding interaction, a metal-metal bonding interaction,
an ionic bonding interaction, a Van der Waals interaction, a
Coulombic attractive interaction, a magnetic interaction, and
combinations thereof, or any other adhesive interaction known to a
person of ordinary skill in the art. In some embodiments, a bottom
layer of a coating of the present invention can be affixed to a
substrate using a contact layer, an epoxy, a resin, a solder, a
mineral, and combinations thereof.
[0172] In some embodiments, a contact layer having a similar
composition to the composition of nanowires in a layer thereon is
present between the substrate and the nanowire coating. For
example, a substrate comprising a layer of aligned zirconium oxide
nanowires thereon can include a thin layer of zirconium oxide
between the substrate and the first layer of nanowires. Thus,
suitable contact layer compositions for use with the present
invention include the same materials listed herein as suitable
materials for use as nanowires. A contact layer can be deposited by
known methods suitable for conformal deposition such as, but not
limited to, chemical vapor deposition, plasma-enhanced chemical
vapor deposition, thermal deposition, sputtering, a molecular beam,
spin-coating, and the like.
[0173] In some embodiments, a contact layer has a thickness of
about 10 nm to about 1 .mu.m, about 25 nm to about 500 nm, about 30
nm to about 300 nm, about 40 nm to about 250 nm, or about 50 nm to
about 200 nm.
[0174] In some embodiments, a bottom layer of nanowires has a
refractive index of about 30% to about 100%, about 30% to about
90%, about 30% to about 80%, about 30% to about 60%, about 30% to
about 50%, about 50% to about 90%, about 50% to about 80%, about
50% to about 70%, about 70% to about 90%, about 70% to about 80%,
about 90%, about 85%, about 80%, or about 75% of a refractive index
of the substrate.
[0175] In some embodiments, a top-most layer of nanowires has a
refractive index of about 1% to about 40%, about 1% to about 35%,
about 1% to about 30%, about 1% to about 25%, about 1% to about
20%, about 1% to about 15%, about 1% to about 10%, about 5% to
about 40%, about 5% to about 35%, about 5% to about 30%, about 5%
to about 25%, about 5% to about 20%, about 5% to about 15%, about
5% to about 10%, about 10% to about 40%, about 10% to about 35%,
about 10% to about 30%, about 10% to about 25%, about 10% to about
20%, about 20% to about 40%, about 20% to about 35%, or about 20%
to about 30% of the refractive index of the substrate.
[0176] In some embodiments, the refractive index of the three or
more laminar layers decreases by about 15% or more per layer, about
20% or more per layer, about 25% or more per layer, about 30% or
more per layer, about 35% or more per layer, about 40% or more per
layer, about 45% or more per layer, or about 50% or more per layer
from the bottom layer of nanowires to the top-most layer of
nanowires.
[0177] FIG. 1A provides a graphic representation of refractive
index versus coating thickness for an ideal gradient refractive
index coating. Referring to FIG. 1A, a line graph, 100, displays
the refractive index versus elevation (e.g., depth or distance) in
arbitrary units ("a.u."). A first portion of the line graph, 101,
corresponds to a substrate, which has a refractive index, 102, and
an elevation (e.g., depth) indicated by the position of line 103. A
second portion of the line graph, 104, corresponds to atmosphere
(i.e., an ambient species proximate to a substrate having an
anti-reflective coating thereon, and typically having a refractive
index less than that of a substrate), which has a refractive index,
105, that is less than a refractive index of the substrate. The
atmosphere has an elevation indicated by the position of line 106,
which corresponds to the elevation of an outer surface of an
anti-reflective coating that is present on the substrate. The
anti-reflective coating has a depth indicated by the magnitude of
vector 107. The presence of an ideal gradient refractive index
coating on the substrate is indicated by the decrease in refractive
index through the depth of the grating. The refractive index of the
ideal anti-reflective coating decreases continuously from the
surface of the substrate (i.e., the base of the coating), 103, to
the outer surface of the coating, 106. The refractive index of the
coating is first matched, 108, at its base to the refractive index
of the substrate, and the refractive index of the coating is also
matched at its surface, 109, to the refractive index of the
atmosphere.
[0178] Not being bound by any particular theory, the refractive
index matching of the anti-reflective coating with, at the base of
the coating, the refractive index of a substrate, and at the
surface of the coating, the refractive index of an atmosphere is
the primary means by which the coatings of the present invention
prevent reflection of electromagnetic radiation from the surface of
a substrate. The coatings of the present invention, can be
optimized for virtually any substrate for use in virtually any
atmosphere because the refractive index of nanowires can be tuned
based on both composition and the density of nanowires in a coating
layer. For example, the anti-reflective coatings of the present
invention can be designed for use in a gaseous atmosphere (e.g.,
air, nitrogen, argon, oxygen, carbon dioxide, and the like) that
typically has a refractive index of about 1.0. The anti-reflective
coatings of the present invention can also be designed for use in a
gaseous atmosphere (e.g., water, or another solvent). For example,
an anti-reflective coating can be designed for use on a submersible
vehicle, a coating designed to mitigate detection by radar, or a
coating designed to minimize reflections from the surface of an
optical window, a cuvette, and the like. An anti-reflective coating
of the present invention can also be tailored to minimize
reflections between solid surfaces. For example, an anti-reflective
coating can be designed to minimize reflections between a lasing
medium and a second solid, between an optical fiber and an output
coupler or an input coupler, and the like.
[0179] FIG. 1B provides a graphic representation of refractive
index versus coating depth or thickness for an anti-reflective
coating of the present invention. Referring to FIG. 1B, a line
graph, 100, displays the refractive index versus elevation. A first
portion of the line graph, 111, corresponds to a substrate, which
has a refractive index, 112, and an elevation indicated by the
position of line 103. A second portion of the line graph, 114,
corresponds to an atmosphere having a refractive index, 115, that
is less than a refractive index of the substrate. The atmosphere
has an elevation indicated by the position of line 106, which
corresponds to the elevation of an outer surface of an
anti-reflective coating that is present on the substrate. The
anti-reflective coating comprises five laminar layers of nanowires,
117, each laminar layer having a thickness indicated by the
magnitude of vectors 121, 122, 123, 124 and 125, respectively. In
some embodiments, the thickness of individual layers of nanowires
within the anti-reflective coating is varied, as shown in FIG. 1B.
The first layer of nanowires, having a thickness equal to the
magnitude of vector 121, has a refractive index substantially
identical to the refractive index of the substrate, 112. Thus, the
anti-reflective coating is refractive index matched with the
substrate, as indicated by arrow 118. The second layer of
nanowires, having a thickness equal to the magnitude of vector 122,
has a refractive index, 132, which is less than the refractive
index of the first layer of nanowires, 112. The third layer of
nanowires, having a thickness equal to the magnitude of vector 123,
has a refractive index, 133, that is less than the refractive index
of the second layer of nanowires. The fourth layer of nanowires,
having a thickness equal to the magnitude of vector 124, has a
refractive index, 134, that is less than the refractive index of
the third layer of nanowires. The fifth layer of nanowires, having
a thickness equal to the magnitude of vector 125, has a refractive
index, 135, that is less than the refractive index of the fourth
layer of nanowires. The refractive index of the fifth layer of
nanowires, 135, is slightly greater than the refractive index of
the atmosphere, 115. The interface between the outer surface of the
anti-reflective coating and the atmosphere is indicated by arrow
119.
[0180] In some embodiments, the refractive index of the three or
more laminar layers of nanowires decreases alinearly from the base
of a coating to the surface of a coating. As used herein,
"alinearly" refers to a coating for which an (x,y) plot of
refractive index versus coating and substrate elevation (e.g.,
thickness) is described or substantially fit by a non-linear curve
(e.g., a quadratic equation, an exponential equation, a power
series, etc.). For example, referring to FIG. 1B, the points
describing the refractive index versus elevation for the
anti-reflective coating, using the elevation of the substrate as
the origin, are fit by a non-linear line, 130.
[0181] FIG. 1C provides a graphic representation of refractive
index versus coating depth or thickness for a second
anti-reflective coating of the present invention. Referring to FIG.
1C, a line graph, 140, displays the refractive index versus
elevation. A first portion of the line graph, 141, corresponds to a
substrate, which has a refractive index, 142, and an elevation
indicated by the position of line 103. A second portion of the line
graph, 144, corresponds to an atmosphere having a refractive index,
145, that is less than a refractive index of the substrate. The
atmosphere has an elevation indicated by the position of line 106,
which corresponds to the elevation of an outer surface of an
anti-reflective coating that is present on the substrate. The
anti-reflective coating comprises three laminar layers of
nanowires, 147, each laminar layer having a thickness indicated by
the magnitude of vectors 151, 152 and 153, respectively. In some
embodiments, the thickness of individual layers of nanowires within
the anti-reflective coating is substantially the same, as shown in
FIG. 1C. The first layer of nanowires, having a thickness equal to
the magnitude of vector 151, has a refractive index, 161, which
less than the refractive index of the substrate, 142. The
substrate-coating interface is indicated by arrow 148. The second
layer of nanowires, having a thickness equal to the magnitude of
vector 152, has a refractive index, 162, which is less than the
refractive index of the first layer of nanowires, 161. The third
layer of nanowires, having a thickness equal to the magnitude of
vector 153, has a refractive index, 163, that is less than the
refractive index of the second layer of nanowires. The refractive
index of the third layer of nanowires, 163, is greater than the
refractive index of the atmosphere, 145. The interface between the
outer surface of the anti-reflective coating and the atmosphere is
indicated by arrow 149.
[0182] In some embodiments, the refractive index of the three or
more laminar layers of nanowires decreases linearly from the bottom
layer of nanowires to the top-most layer of nanowires. As used
herein, "decreases linearly" refers to a coating for which an (x,y)
plot of refractive index versus coating and substrate elevation
(e.g., thickness) is described or substantially fit by a linear
equation. For example, referring to FIG. 1C, the points describing
the refractive index versus elevation for the anti-reflective
coating, using the elevation of the substrate as the origin, are
fit by a straight line, 150.
[0183] FIG. 2 provides a three-dimensional cross-sectional
representation, 200, of one embodiment of an anti-reflective
coating of the present invention. Referring to FIG. 2, a substrate,
201, is provided having an arrangement of nanowires, 202, thereon.
The nanowires have a lateral dimension (e.g., a width or a
diameter) indicated by the magnitude of vector 203, and a vertical
dimension (e.g., a height or a second diameter) indicated by the
magnitude of vector 204. The portion of the nanowires that is
visible in the schematic representation has a length indicated by
the magnitude of vector 205. The nanowires in contact with or
affixed to the substrate form a first laminar layer (e.g., a bottom
layer) of nanowires on the substrate, 206. The anti-reflective
coating further includes a second layer of nanowires, 207, a third
layer of nanowires, 208, a fourth layer of nanowires, 209, a fifth
layer of nanowires, 210, a sixth layer of nanowires, 211, a seventh
layer of nanowires, 212, an eighth layer of nanowires, 213, a ninth
layer of nanowires, 214, a tenth layer of nanowires, 215, an
eleventh layer of nanowires, 216, a twelfth layer of nanowires,
217, a thirteenth layer of nanowires, 218, a fourteenth layer of
nanowires, 219, and a fifteenth layer of nanowires, 220.
[0184] In some embodiments, a thickness of a laminar layer within a
multi-layer coating of nanowires is approximately a diameter of a
nanowire present within the laminar layer. In some embodiments, a
thickness of a laminar layer within a multi-layer coating of the
present invention is about two times or less, about three times or
less, about five times or less, or about ten times or less than an
average diameter of a nanowire present within the layer of
nanowires. Referring to FIG. 2, the individual layers of nanowires
depicted have a thickness substantially identical to the diameter
of the nanowires. The nanowires in the various layers of the
anti-reflective coating can have diameters, heights and widths that
are substantially identical or different.
[0185] The orientation of a nanowire relative to a substrate
surface can be described by a "pitch", which as used herein refers
to an average angle made between a long axis of a nanowire and the
plane of a substrate (or for non-planar substrates, with an average
curvature of the substrate). Referring to FIG. 2, the pitch of
layers 206, 208, 210, 212, 214, 216, 218 and 220 is described by
angle .PSI., wherein 0.degree. is described by co-planarity with a
substrate. The pitch of layers 207, 209, 211, 213, 215, 217 and 219
is described by angle .PHI., wherein 0.degree. is described by
co-planarity with a substrate. In some embodiments, nanowires
present within a layer of an anti-reflective coating have a pitch
of about .+-.30.degree., about .+-.25.degree., about
.+-.20.degree., about .+-.15.degree., about .+-.10.degree., about
.+-.5.degree., or about 0.degree.. In some embodiments, the long
axis of the nanowires present within a layer are substantially
co-linear or co-planar with a plane of a substrate, i.e., have a
pitch of about 0.degree.; for example, when a laminar layer of
nanowires has a thickness that is substantially identical to an
average diameter of nanowires present within the layer.
[0186] In some embodiments, adjacent nanowires within a laminar
layer of a coating are oriented in a non-random manner. The
orientation relative to one another of any two adjacent nanowires
within a layer can be described by an angle formed between two
vectors oriented co-linear to long axes of the nanowires. Referring
to FIG. 2, adjacent nanowires 221 and 222, present within layer
220, are oriented relative to one another by an angle
.THETA..sub.i. Adjacent nanowires 222 and 223, present within layer
220, are oriented substantially parallel to one another. In some
embodiments, nanowires present within the same layer are oriented
at an average angle of about 30.degree. or less, about 25.degree.
or less, about 20.degree. or less, about 15.degree. or less, about
10.degree. or less, or about 5.degree. or less relative to other
nanowires present within the layer. In some embodiments, nanowires
within a single laminar layer of a coating of the present invention
are oriented substantially parallel to one another.
[0187] In some embodiments, adjacent nanowires within a single
laminar layer of a coating of the present invention are in contact
with one another, for example, at a point or points along the long
axes of the nanowires. In some embodiments, adjacent nanowires
within a single laminar layer do not substantially contact one
another. Referring to FIG. 2, adjacent nanowires 223 and 224,
present within layer 220, do not contact one another and have a
spacing there between indicated by the magnitude of vector 225. In
some embodiments, adjacent nanowires within a layer have a spacing
there between of about 30% or less, about 25% or less, about 20% or
less, about 15% or less, about 10% or less, or about 5% or less
than the average length of the nanowires present in the layer.
[0188] In some embodiments, nanowires within adjacent laminar
layers of a coating are oriented in a non-random manner. The
orientation relative to one another of any two nanowires within
adjacent layers can be described by an angle formed between two
vectors oriented co-linear to long axes of the nanowires. Referring
to FIG. 2, nanowires 221 and 230, present within adjacent layers
220 and 219, respectively, are oriented relative to one another by
an angle .THETA..sub.a1.
[0189] In some embodiments, nanowires within adjacent laminar
layers of the multi-layer coating are substantially orthogonal to
one another. For example, nanowires 222 and 230, present within
adjacent coating layers 220 and 230, respectively, are oriented
substantially orthogonal to one another (i.e., are oriented
relative to one another by an angle .THETA..sub.a2, which is about
90.degree..
[0190] In some embodiments, the refractive index of a multi-layer
coating can be decreased without adjusting the number density of
nanowires in adjacent layers of the coating. Specifically, porous
nanowires having diameters of varying size that include an internal
void space can be utilized to provide multi-layer GRIN coatings.
Porous nanowires having a controlled porosity (and a controlled
refractive index) deposited in aligned layers by the methods
described herein to provide aligned nanowire coatings having a
controlled refractive index. Generally, for nanowires of similar
chemical composition, increasing the porosity results in a decrease
in the refractive index of the nanowires. Thus, the present
invention is directed to a GRIN multi-layer coating in which a
constant number density of nanowires per coating layer is
maintained, while the refractive index of the nanowire coating
layers is decreased by increasing the porosity or changing the
composition of the nanowires in the layers of the coating. The
present invention is also directed to multi-layer coatings in which
both the number density of nanowires and porosity or chemical
composition of nanowires is varied between adjacent coating layers
to provide a multi-layer GRIN coating structure.
[0191] In some embodiments, a coating further comprises a molecular
or polymeric matrix surrounding the multi-layer coating of
nanowires, wherein at least a portion of the top-most layer of
nanowires is exposed. Preferred polymers include structures having
narrow and/or low-intensity absorptions in the near-infrared and/or
infrared regions of the spectrum. For example, polymers comprising
carbon-carbon (C--C) bonds, carbon-hydrogen (C--H) bonds, ether
(C--O) bond, carbonyl (C.dbd.O) bonds, carbon-halogen (C--X) bonds
wherein X is preferably --F or --Cl, and the like are particularly
suitable for encapsulating at least a portion of a nanowire coating
of the present invention.
[0192] In some embodiments, a polymer suitable for use as an
encapsulant can be dissolved in a solvent for application via
drop-coating, spin-coating, spray-coating, dip-coating, and the
like. Therefore polymers capable of being dissolved in a solvent
selected from: a hydrocarbon (e.g., hexanes, and the like), an
aromatic solvent (e.g., toluene, benzene, and the like), a
nitrogen-containing solven (e.g., pyridine, and the like), acetone,
ethyl acetate, a nitrile solvent (e.g., acetonitrile,
butyronitrile, and the like), dimethylformamide, diethylacetamide,
N-methylpyrrolidone, a chlorinated solvent (e.g., chloroform,
methylene chloride, dichloroethane, and the like), an ether, a
glycol, a glycol ether, and the like, and combinations thereof.
[0193] In some embodiments, a polymer suitable for use as an
encapsulant of a nanowire coating of the present invention is
selected from a polyolefin (e.g., an ethylene-alkylene copolymer
such as ethylene-butylene copolymer, and the like), ethylene-vinyl
acetate copolymers, styrene polymers, halogenated hydrocarbon
polymers, vinyl polymers, acrylic polymers, methacrylic polymers,
polyethers, polyether copolymers, polyamides, polyimines,
polyurethanes, polysiloxanes, cellulosic polymers, and combinations
thereof. In some embodiments, an encapsulant comprises a
high-molecular weight polystyrene (e.g., polystyrene having a
molecular weight of about 100,000 Da to about 1,000,000 Da), a
vinyl polymer, or a (styrene-ethylene-butylene) tri-block copolymer
grafted with maleic anhydride.
[0194] In some embodiments, an encapsulant comprises a ceramic.
Ceramics deposited from a sol-gel process are particularly useful,
and include, but are not limited to, zirconia, titania, alumina,
and the like, a doped variant thereof, and combinations thereof.
Precursor mixtures suitable for depositing a ceramic from a sol-gel
process include, but are not limited to, Zr(OR).sub.x(OH).sub.y,
Ti(OR).sub.x(OH).sub.y, Al(OR).sub.x(OH).sub.y, and combinations
thereof, wherein R is independently at each occurrence a
C.sub.1-C.sub.6 alkyl, the mixtures can comprise a single precursor
or a mixture of precursors having different substituents wherein x
in the mixture is 0 to 2, y in the mixture is 0 to 2 and x+y=2 (for
Zr- and Ti-containing precursors), and x in the mixture is 0 to
1.5, y in the mixture is 0 to 1.5, and x+y=1.5 (for Al-containing
precursors).
[0195] The present invention is also directed to a composition,
comprising: a substrate including a surface and having on at least
a portion of the surface an anti-reflective multi-layer mat of
nanowires comprising three or more laminar layers of nanowires and
including a bottom layer of nanowires affixed to the surface and a
top-most layer of nanowires, wherein the top-most layer of
nanowires has a refractive index of about 5% to about 70% of a
refractive index of the bottom layer of nanowires, and wherein the
refractive index of the three or more laminar layers decreases by
about 10% or more per layer from the bottom layer of nanowires to
the top-most layer of nanowires.
[0196] As used herein, a "mat" refers to a coating comprising
multiple layers of nanowires either from a single deposition
process in which adjacent nanowires are partially entangled with
one another, thereby providing a single layer having a thickness
greater than an average diameter of the nanowires or multiple
layers of optionally aligned nanowires having a pitch of about
.+-.60.degree. or less.
[0197] In some embodiments, a thickness of a laminar layer within a
mat of nanowires is about 10 times or less, about 5 times or less,
about 4 times or less, about 3 times or less, about 2 times or
less, or about 1.5 times or less an average diameter of the
nanowires present within the laminar layer of the mat. The
thicknesses of the laminar layers present within the mat can be
same or independently varied.
[0198] In some embodiments, the substrate and the metallic
nanowires comprise at least one metal that can be the same or
different selected from: a transition metal, a Group 13 metal, a
Group 14 metal, a Group 15 metal, an oxide thereof, or a
combination thereof. In some embodiments, particularly suitable
metals for use as a substrate and/or a nanowire have a limited
absorbance in the near-IR and/or IR region of the electromagnetic
spectrum (e.g., from about 1 .mu.m to about 30 .mu.m). In some
embodiments, a substrate and/or a nanowire is a metal selected
from: silicon, germanium, gallium, indium, an arsenide thereof, a
selenide thereof, a silicide thereof, and combinations thereof. In
some embodiments, the metallic nanowires within the multi-layer mat
are bound to the substrate and each other via metal-metal bonds.
Bonding can be achieved and/or enhanced, for example, via
sintering, calcining, soldering, plasma treating, welding, and
combinations thereof.
[0199] In some embodiments, the present invention is directed to a
composition, comprising: a ZnS substrate including a surface, and a
multi-layer coating of ZnS nanowires positioned on at least a
portion of the surface, the coating comprising three or more
laminar layers of ZnS nanowires, including a bottom layer of ZnS
nanowires affixed to the surface, and a top-most layer of ZnS
nanowires, wherein a ZnS nanowire within a laminar layer is
oriented substantially parallel to another ZnS nanowire within the
same laminar layer, ZnS nanowires within adjacent laminar layers
are not substantially parallel to one another, the top-most layer
of ZnS nanowires has a refractive index of about 5% to about 70% of
a refractive index of the bottom layer of ZnS nanowires, and the
refractive index of the three or more laminar layers of ZnS
nanowires decreases by about 10% or more per laminar layer from the
bottom layer of ZnS nanowires to the top-most layer of ZnS
nanowires.
[0200] In some embodiments, the resistance to crack propagation
(e.g., fracture toughness) of a substrate is improved by coating
with a multi-layer nanowire coating of the present invention. As
opposed to the incorporation of inorganic or metal fibers or
nanowires into a substrate, the present invention provides a method
of improving the crack resistance of a substrate without modifying
its composition.
[0201] Not being bound by any particular theory, a nanowire coating
of the present invention can improve the fracture resistance by
improving load distribution from the substrate to the nanowire
coating, as well as, under certain conditions, absorbing shock from
high-velocity, particles and liquids. For example, the coatings of
the present invention can be utilized as resistance coatings for
spaceships, airships, airplanes, jets, munitions (e.g., missiles,
bombs, rockets, and the like), as well as automotive parts, and any
other application in which anti-reflection, abrasion resistance and
crack resistance are desirable.
[0202] In some embodiments, the nanowire coatings of the present
invention are of particular use for improving the crack resistance
and durability of ceramic substrates (e.g., zinc sulfide and doped
variants thereof). Crack resistance can be measured using, e.g., a
nanoindenter, or any other analytical method known to a person of
ordinary skill in the art.
[0203] In some embodiments, a portion of the substrate having a
nanowire coating of the present invention thereon has a resistance
to crack propagation that is about 3 times or more, about 5 times
or more, about 7 times or more, about 10 times or more, or about 12
times or more than a portion of the metallic substrate surface that
lacks the multi-layer coating of nanowires.
[0204] In some embodiments, at least a portion of the substrate
having a nanowire coating of the present invention thereon has a
durability, wear- and/or abrasion-resistance that is about 3 times
or more, about 5 times or more, about 7 times or more, or about 10
times or more than a portion of the metallic substrate surface that
lacks the nanowire coating. Durability, wear- and/or
abrasion-resistance can be measured, for example, using a water-jet
impact test, a sand drop test, a scratch test, or any other
durability, wear- and/or abrasion-resistance test known to persons
of ordinary skill in the art.
[0205] The present invention is also directed to a composition,
comprising: a substrate including a surface and an anti-reflective
multi-layer coating positioned on at least a portion of the
surface, the coating comprising three or more laminar layers, each
layer comprising a matrix incorporating a different degree of
porosity compared to the other layers in the coating, wherein a
bottom layer of the coating is affixed to the surface, wherein the
bottom layer has a refractive index of about 60% to about 100% of a
refractive index of the substrate, wherein a top-most layer of the
coating has a refractive index of about 1% to about 40% of the
refractive index of the substrate, and wherein the refractive index
of the three or more laminar layers decreases by about 10% or more
per layer from the bottom layer of the coating to the top-most
layer of the coating.
[0206] As used herein, a "matrix" refers to a material capable of
forming a film or coating on a substrate. Materials suitable for
use as a matrix with the present invention include, but are not
limited to, polymers, glasses (e.g., inorganic and organic-doped
oxides), crystalline and polycrystalline materials (e.g., quartz),
and combinations thereof. In some embodiments, the matrix comprises
one or more polymers selected from: a polystyrene, a polysiloxane,
a polyacrylate, a polyvinylpyrrolidone, a polycarbonate, a
polyalkyleneglycol, a (styrene-ethylene-butylene) tri-block
copolymer grafted with maleic anhydride, a substituted variant
thereof, or a combination thereof.
[0207] In some embodiments, materials suitable for use as a matrix
have a maximum refractive index, n.sub.M, of about 20, about 15,
about 10, about 5, about 2, or about 1.5. In some embodiments,
materials suitable for use as a matrix have a minimum refractive
index, n.sub.M, of about 1.4, about 1.5, about 1.8, or about 2.
[0208] In some embodiments, a matrix has a glass transition
temperature of about 400.degree. C. to about 1000.degree. C. In
some embodiments, a matrix has a minimum glass transition
temperature of about 400.degree. C., about 425.degree. C., about
450.degree. C., about 500.degree. C., about 550.degree. C., about
600.degree. C., about 700.degree. C., or about 800.degree. C. In
some embodiments, a matrix has a maximum glass transition
temperature of about 1000.degree. C., about 950.degree. C., about
900.degree. C., about 850.degree. C., or about 800.degree. C.
[0209] As used herein, a "pore-forming moiety" refers to a
composition having a mean diameter of about 1 nm to about 100 nm.
In some embodiments, a pore-forming moiety has a maximum mean
diameter of about 100 nm, about 90 nm, about 80 nm, about 70 nm,
about 60 nm, about 50 nm, about 40 nm, about 30 nm, about 25 nm,
about 20 nm, about 18 nm, about 15 nm, about 12 nm, about 10 nm,
about 8 nm, about 5 nm, or about 2 nm. In some embodiments, a
pore-forming moiety has a minimum mean diameter of about 1 nm,
about 1.5 nm, about 2 nm, about 2.5 nm, about 3 nm, 4 nm, about 5
nm, about 10 nm, or about 20 nm. Pore-forming moieties for use with
the present invention are not limited to primarily spherical
materials, but can have any three-dimensional shape such as, but
not limited to, ellipsoidal, cylindrical, conical, polyhedral,
toroidal, and combinations thereof. For non-spherical pore-forming
moieties for use with the present invention, the mean diameter is
equivalent to the longest axis of the three-dimensional
pore-former.
[0210] As used herein, a "loading" refers to the volume of a layer
occupied by a pore-forming moiety. As used herein, a "porosity"
refers to the volume of a layer occupied by void space introduced
by a pore-forming moiety. In some embodiments, a layer of a coating
of the present invention has a particulate loading and/or porosity
of about 20% to about 95%. In some embodiments, a layer of a
coating of the present invention has a maximum particulate loading
and/or porosity of about 95%, about 92%, about 90%, about 88%,
about 85%, about 82%, about 80%, about 78%, about 75%, about 70%,
or about 65%. In some embodiments, a layer of a coating of the
present invention has a minimum particulate loading and/or porosity
of about 20%, about 25%, about 30%, about 35%, about 40%, about
45%, about 50%, about 55%, about 60%, about 65%, about 70%, or
about 75%.
[0211] In some embodiments, in addition to being anti-reflective
the coatings of the present invention are smudge resistant. As used
herein, a "smudge" refers to a residue that can be deposited on a
film surface. A residue can include dirt, a particulate (e.g.,
diesel exhaust, soot, and the like), an oil (e.g., a composition
that is immiscible with water), a vapor (e.g., water and steam, as
well as environmental vapors such as fog, clouds, smog, and the
like), a component of human and/or animal perspiration (e.g., an
exudate from the apocrine glands, merocrine glands, sebaceous
glands, and the like), oils produced by the hair and/or skin of
human and/or animal, other biological compositions (e.g., saliva,
blood, skin flakes, hair, excrement, other waste, and the like),
and combinations thereof.
[0212] Not being bound by any particular theory, the refractive
index of smudges is typically different than that of a film
material. Thus, in addition to any light-blocking debris present in
the smudge, this difference in refractive index between the smudge
and the underlying substrate is what makes the smudge visible to a
viewer, and can give a smudge an "oily" appearance, especially when
deposited onto a smooth surface. However, a roughened surface both
diffracts and diffuses light emerging and/or reflecting from the
surface. Thus, a smudge deposited onto a roughened surface will
induce less of a change in the pattern of light emerging and/or
reflected from the roughened surface. Moreover, a roughened surface
presents peaks and valleys (that can be in a regular pattern or in
a random arrangement upon the surface) that can sequester a smudge
material, such that a smudge deposited on a surface does not lead
to a conformal deposition of smudge residue upon the surface. For
example, the valleys of a roughened surface can remain comparably
"smudge free", whereas the peaks of a roughened surface can
sequester the smudge material. Alternatively, the peaks of a
roughened surface can remain comparably "smudge free", whereas the
valleys of a roughened surface can sequester the smudge
material.
[0213] As used herein, "roughness" refers to a topography of a
surface of a coating as measured by the root-mean square (rms) of
the surface variations. The rms roughness of a surface is based on
finding a median level for a surface of a coating and evaluating
the standard deviation from this median level. The rms roughness,
R, for a surface can be calculated using equation (3):
R = 1 N 2 i = 1 N j = 1 N ( H ( i , j ) - H _ ) 2 ( 3 )
##EQU00001##
wherein i and j describe a location on the surface, H is the
average value of the height across the entire surface of a coating,
and N is the number of data points sampled on the surface of the
coating.
[0214] In some embodiments, a coating of the present invention has
a surface roughness of about 100 nm to about 10 .mu.m, about 200 nm
to about 10 .mu.m, about 500 nm to about 10 .mu.m, about 1 .mu.m to
about 10 .mu.m, about 2 .mu.m to about 10 .mu.m, about 5 .mu.m to
about 10 .mu.m, about 1 .mu.m, about 2 .mu.m, about 5 .mu.m, or
about 10 .mu.m. In some embodiments, a coating of the present
invention has a surface roughness approximately equal the diameter
of the nanowires present in the outermost layer of a multi-layer
coating. In some embodiments, a coating of the present invention
can be roughened by one or more post-deposition treatment
processes.
[0215] In some embodiments, a portion of a substrate having an
anti-reflective coating of the present invention thereon reflects
about 50% or less, about 40% or less, about 30% or less, about 20%
or less, about 15% or less, about 10% or less, about 5% or less,
about 2% or less, about 1% or less, about 0.5% or less, about 0.1%
or less, about 0.05% or less, about 0.01% or less, about 0.005% or
less, about 0.001% or less, or about 0.0005% or less of at least
one wavelength of an electromagnetic radiation having at least one
wavelength of about 180 nm to about 30 .mu.m compared to an
uncoated portion of the substrate. In some embodiments, a portion
of a substrate having the anti-reflective multi-layer coating of
nanowires thereon reflects about 50% or less of at least one
wavelength of an electromagnetic radiation having at least one
wavelength of about 180 nm to about 30 .mu.m, about 180 nm to about
10 .mu.m, about 180 nm to about 1 .mu.m, about 180 nm to about 500
nm, about 180 nm to about 400 nm, about 180 nm to about 300 nm,
about 180 nm to about 250 nm, about 250 nm to about 30 .mu.m, about
250 nm to about 10 .mu.m, about 250 nm to about 1 .mu.m, about 250
nm to about 500 nm, about 250 nm to about 400 nm, about 300 nm to
about 30 .mu.m, about 300 nm to about 10 .mu.m, about 300 nm to
about 1 .mu.m, about 400 nm to about 30 .mu.m, about 400 nm to
about 10 .mu.m, about 400 nm to about 5 .mu.m, about 400 nm to
about 1 .mu.m, about 1 .mu.m to about 30 .mu.m, about 5 .mu.m to
about 30 .mu.m, or about 10 .mu.m to about 30 .mu.m compared to an
uncoated portion of the substrate.
[0216] In some embodiments, a substrate coated with a nanowire
coating of the present invention has a reduced retro-reflectance
compared with an uncoated substrate. As used herein,
"retro-reflectance" refers to light that is reflected from a
substrate back to its source along a vector that is parallel to,
but in the opposite direction of the incoming light. Generally,
retro-reflected light is not substantially scattered by a
substrate. Many substrates that are transparent in the
near-infrared and/or infrared regions of the spectrum are
retro-reflective in the visible region of the electromagnetic
spectrum. The nanowire coatings of the present invention are
suitable for reducing, or substantially eliminating
retro-reflection for many substrates, including substrates that are
substantially transparent in the near-IR and/or IR regions of the
electromagnetic spectrum.
[0217] Thus, in some embodiments, a substrate having the multilayer
mat or coating of nanowires thereon has a retro-reflectance at one
or more wavelengths from about 400 nm to about 12 .mu.m that is at
least 50% less, at least 60% less, at least 70% less, at least 80%
less, at least 90% less, or at least 95% less than a
retro-reflectance from an uncoated substrate that lacks the
multilayer mat of nanowires at the same one or more
wavelengths.
[0218] In particular, in some embodiments, a substrate having a
multilayer mat or coating of nanowires thereon has a
retro-reflectance at 633 nm that is at least 50% less, at least 60%
less, at least 70% less, at least 80% less, at least 90% less, or
at least 95% less than a retro-reflectance at 633 nm from an
uncoated substrate that lacks the multilayer coating of
nanowires.
[0219] The present invention is directed to a zinc sulfide,
germanium, sapphire, or silicon substrate having a GRIN coating of
the present invention thereon, wherein the transmittance of the
substrate is reduced by about 10% or less at a wavelength from 1
.mu.m to 12 .mu.m, and wherein the retro-reflectance of the
substrate is decreased by about 50% or more, 60% or more, 70% or
more, 80% or more, 90% or more, or 95% or more at a wavelength from
about 400 nm to about 800 nm compared with the retro-reflectance of
an uncoated ZnS substrate at the same wavelength from about 400 nm
to about 800 nm.
[0220] The anti-reflective coatings of the present invention are
robust. As used herein, "robust" refers to physical, dimensional
and/or chemical stability. For example, the coatings of the present
invention exhibit wear resistance, dimensional stability, and
chemical stability that makes them suitable for use in environments
under which the coatings are subjected to physical contact,
mechanical stress, chemical reactivity and/or exposure to intense
electromagnetic radiation.
[0221] In some embodiments, a coating of the present invention has
a Young's Modulus of about 1 GPa to about 1,000 GPa, about 10 GPa
to about 1,000 GPa, about 50 GPa to about 1,000 GPa, about 100 GPa
to about 1,000 GPa, or about 500 GPa to about 1,000 GPa. In some
embodiments, the Young's Modulus of a coating of the present
invention is substantially the same as the Young's Modulus the
nanowires present in the layers of the coating, or the matrix
present in the layers of the coating.
[0222] In some embodiments, a thin layer can be deposited over a
coating and/or an outer surface of a coating can be derivatized to
provide a barrier to detritus, chemical contamination, increase the
mechanical strength of a coating, provide enhanced smudge
resistance, and the like.
Processes to Prepare the Anti-reflective Coatings
[0223] The processes of the present invention are suitable to
deposit an anti-reflective coating in any geometry that is desired.
In some embodiments, a conformal anti-reflective coating is
deposited. As used herein, "conformal" refers to a layer or coating
that is of substantially uniform thickness regardless of the
geometry of underlying features. Thus, conformal coating of
substrates of various size and shape can result in anti-reflective
coatings having substantially similar sizes and shapes, and the
size of the resulting articles can be controlled by selecting the
dimensions of a substrate (e.g., the spacing and dimensions of a
grating, or shape of a touch-screen, and the like).
[0224] The present invention is also directed to a process for
preparing an anti-reflective multi-layer nanowire coating on at
least a portion of a surface of a substrate, the process
comprising:
[0225] disposing on the surface a first laminar layer of nanowires,
wherein the first laminar layer has a refractive index about 60% to
about 100% of a refractive index of the substrate;
[0226] affixing the first laminar layer of nanowires to the
surface;
[0227] disposing a second laminar layer of nanowires onto the first
laminar layer of nanowires;
[0228] affixing the second laminar layer of nanowires to the first
laminar layer of nanowires;
[0229] disposing at least a third laminar layer of nanowires onto
the second laminar layer of nanowires; and
[0230] affixing the third laminar layer of nanowires to the second
laminar layer of nanowires; wherein the second laminar layer of
nanowires has a refractive index less than the refractive index of
the first laminar layer of nanowires, and wherein the third laminar
layer of nanowires has a refractive index less than the refractive
index of the second laminar layer of nanowires.
[0231] As used herein, "disposing" refers to any process whereby
nanowires are formed on a substrate. Disposing processes can be
additive (i.e., material is added to a surface) or subtractive
(i.e., material is removed from a surface), or a combination
thereof. Disposing can be performed serially or in parallel, either
of which processes can include self assembly of a material onto a
substrate. In some embodiments, disposing refers to disposing an
arrangement of nanowires on a substrate. Disposing processes can
include, but are not limited to, depositing (e.g., via dip-coating,
electrospinning, printing, stamping, and the like), growing, and
combinations thereof.
[0232] In some embodiments, disposing a first layer of nanowires on
a substrate comprises growing a first layer of nanowires on the
substrate. Any process suitable for growing nanowires known to a
person of ordinary skill in the art can be used. For example, in
some embodiments a first layer of nanowires is catalytically grown
on a substrate.
[0233] In some embodiments, a process of the present invention
comprises activating a surface of a substrate. As used herein,
"activating" refers to treating a substrate prior to, or
concomitant with, disposing to enhance the quality of a deposition
process (e.g., provide enhanced yield, a faster deposition rate, a
more controlled deposition process). Activating can include,
without limitation, cleaning, reducing, oxidizing, functionalizing,
derivatizing, polishing, roughening, plasma treating, thermally
treating, and combinations thereof. In some embodiments, activating
comprises removing a native oxide layer from a surface of a
conductive and/or semiconductive substrate.
[0234] In some embodiments, the process further comprises:
[0235] aligning the nanowires within the first laminar layer to
orient the nanowires substantially parallel to one another;
[0236] aligning the nanowires within the second laminar layer to
orient the nanowires within the second laminar layer substantially
parallel to one another, wherein the nanowires within the second
laminar layer are not parallel to the nanowires within the first
laminar layer; and
[0237] aligning the nanowires within the third laminar layer to
orient the nanowires within the third laminar layer substantially
parallel to one another, wherein the nanowires within the third
laminar layer are not parallel to the nanowires within the second
laminar layer.
[0238] As used herein, "aligning" refers to controlling the
orientation of a long axis of a nanowire or group of nanowires. In
some embodiments, aligning includes orienting a group of nanowires
such that the long axes of the nanowires are substantially parallel
with one another. In some embodiments, aligning includes orienting
a first group of nanowires such that the long axes of the nanowires
present in the first group are angularly oriented relative to the
long axes of a second group of nanowires. Aligning can refer to
controlling the orientation of nanowires in solution, on a surface
of a stamp, on a substrate, and combinations thereof. In some
embodiments, "aligning" refers to controlling the x,y,z position of
nanowires deposited on a substrate.
[0239] In some embodiments, aligning comprises at least one of:
applying a mechanical force to the nanowires (e.g., alignment on
the surface of an aqueous solution via mechanical force), applying
a magnetic field to the nanowires, applying an electric field to
the nanowires (e.g., using an AC field to induce electric dipole
moments in the nanowires, which induces alignment relative to
electrodes), applying a fluid gradient to the nanowires, and
combinations thereof.
[0240] In some embodiments, a process of the present invention
comprises disposing a fourth laminar layer of nanowires onto a
third laminar layer of nanowires, wherein the fourth laminar layer
of nanowires has a refractive index less than the refractive index
of the third laminar layer of nanowires. Thus, the present
invention includes processes suitable for forming multi-layer
coatings comprising more than three layers, for example, four,
five, six, seven, eight, nine, ten, eleven, twelve, fifteen,
twenty, thirty, forty, fifty, or one hundred or more layers of
nanowires.
[0241] In some embodiments, the process further comprises aligning
nanowires within a fourth laminar layer to orient the nanowires
within the fourth laminar layer substantially parallel to one
another, wherein the nanowires within the fourth laminar layer are
not parallel to the nanowires within the third laminar layer.
[0242] In some embodiments, a bottom layer of nanowires is affixed
to the substrate. In some embodiments, nanowires in adjacent layer
of a multi-layer coating are affixed to each other. Affixing can be
performed during a providing process (e.g., a forming, or a
depositing of the nanowires on a substrate) or via another process
(e.g., a post-treating process). Post-treating processes suitable
for affixing the nanowires to a substrate include, but are not
limited to, calcining, covalently bonding, hydrogen-bonding,
calcining, soldering, cross-linking, melting, encapsulating in a
matrix, and combinations thereof.
[0243] In some embodiments, ordered nanowire layers are deposited
by a fluidic process in which the nanowires are dispersed in a
solution, aligned, and then the aligned nanowires are applied to a
substrate. Nanowires can be rendered hydrophobic via chemical
functionalization, and added to an aqueous solution and dispersed.
Typically, the nanowires float on the surface of the aqueous
solution. Clumping of the nanowires, if present, can be diminished
via sonication, mechanical mixing, heating, and the like.
[0244] In some embodiments, the aqueous solution comprises
distilled water. The aqueous solution can also contain an additive
such as, but not limited to, a salt (e.g., an alkali salt, an
alkali earth metal salt, a metal salt, and the like), an acid
(e.g., a mineral acid, an organic acid, and the like), a base
(e.g., a mineral base, an organic base, and the like), a
surfactant, a polymer, and combinations thereof.
[0245] In some embodiments, the nanowires are dispersed in a
solvent and then added to the aqueous solution to provide a
dispersion. The solvent can be removed from the aqueous solution
via evaporation to provide a film of nanowires on the surface of
the aqueous solution.
[0246] The dispersed nanowires are then aligned by applying an
external force to the nanowires. In some embodiments, the nanowires
are aligned by applying a mechanical force to the enclosure
containing the aqueous dispersion of nanowires such that the
surface area of the aqueous solution decreases. For example,
nanowires are dispersed in trough having adjustable sidewalls,
which are moved towards one another to decrease the surface area of
the aqueous solution (while ends of the trough remain mostly
stationary). Movement of the sidewalls of the trough applies a
mechanical force to the nanowires on the surface of the aqueous
solution and forces the nanowires to align on or near the surface
of the aqueous solution via mechanical contact with the sidewalls
and/or adjacent nanowires. The aligning process can be monitored
using, e.g., a surface tensiometer, which can be maintained in a
feedback loop with a stepper used to control the movement of one or
both of the sidewalls of the enclosure (i.e., the trough).
[0247] In addition to a mechanical force, other forces suitable for
aligning the nanowires on or near the surface of the aqueous
solution include, but are not limited to, a magnetic force (e.g.,
applied to nanowires comprising a material having a dipole moment
or an induced dipole moment), a fluid force (e.g., through the
aqueous solution), and the like, and combinations thereof.
[0248] In those embodiments in which alignment is induced via
mechanical force applied to one or more sides of an enclosure
containing an aqueous dispersion of nanowires, the enclosure a
material suitable for inducing a positive meniscus between the
surface of the aqueous solution the sides of the enclosure.
Suitable materials include hydrophobic materials. In some
embodiments, at least the surface of the enclosure that contacts
the surface of the aqueous solution comprises an optionally
fluorinated perfluorpolyoalkylene (e.g., TEFLON.RTM., E.I. Du Pont
de Nemours and Co., Wilmington, Del.).
[0249] Once a nanowire film on the surface of an aqueous solution
reaches a desired density, the nanowires are transferred to a
substrate through a dip-coating process. As used herein,
"dip-coating" refers to a process in which a substrate is passed
through an aqueous solution comprising nanowires dispersed thereon
and/or therein, and via attractive forces the aligned nanowires
deposit onto the substrate in a self-assembled manner. The nanowire
density on the substrate can be controlled by the density of
nanowires present in the aqueous dispersion. Substrate densities
approaching monolayer coverage can be achieved. A deposited layer
of nanowires can be annealed, sintered, encapsulated, and the like,
followed by deposition of another nanowire layer thereon. The
density of each layer of nanowires deposited by the dip-coating
process can be controlled by the density of nanowires present on
the surface of the aqueous solution.
[0250] Thus, this process can generate a nanowire coating having a
gradient refractive index by compressing a nanowire film to
generate a nearly close-packed layer and transferring the
close-packed layer to the substrate, followed by decreasing the
nanowire density on the surface of the aqueous solution (e.g., by
decreasing the number of nanowires and/or increasing the surface
area of the aqueous solution by moving a sidewall) and applying a
second layer of nanowires (having a lower density that the first
layer of nanowires) to the substrate. The orientation the nanowires
relative to the substrate and to previously deposited aligned
layers of nanowires can be controlled by the orientation of the
substrate during the dip-coating, and rotation of the
substrate.
[0251] The dip-coating process can be repeated until a nanowire
layer having a refractive index of about 1.1 or less has been
deposited. In addition, because the density of nanowires present on
the surface of the aqueous solution can be controlled, multi-layer
nanowire coatings having smooth layer-to-layer transitions in
refractive index can be readily prepared. The dip-coating process
also enables both sides of a substrate to be coated simultaneously
with nanowire coatings.
[0252] Thus, in some embodiments, the present invention is directed
to a process comprising:
[0253] dispersing a plurality of nanowires in a non-aqueous
solvent;
[0254] applying the non-aqueous dispersion of nanowires to an
aqueous solution;
[0255] aligning the nanowires in the aqueous solution; and
[0256] disposing the aligned nanowires from the aqueous solution
onto a substrate.
[0257] In some embodiments, the process further comprises removing
the non-aqueous solvent from the aqueous solution. Embodiments in
which a non-aqueous, water-miscible solvent is not removed from the
aqueous solution prior to the aligning are also within the scope of
the present invention.
[0258] In some embodiments, the aligning is performed with the
nanowires localized on the surface of the aqueous solution.
[0259] In some embodiments, the disposing and/or aligning of
nanowires is performed via an electrospinning process.
Electrospinning processes and nanowires prepared therefrom that are
suitable for use with the present invention are provided in US Pub.
No. 2006/0226580, U.S. Appl. No. 61/227,336, and U.S. Appl. No.
61/240,891, which are incorporated herein by reference in their
entireties.
[0260] Disposing and/or aligning of nanowires on curved substrate
can be readily achieved using an electrospinning process in which a
curved substrate is placed on a stage having comprising a
conductive material, wherein a plurality of conductive lines are
used to support the curved substrate and align the nanowires
deposited thereon. FIG. 11 provides a schematic cross-sectional
representation, 1100, of a electrospinning apparatus suitable for
disposing aligned nanowires on a curved substrate. Referring to
FIG. 11, a spinneret, 1101, comprising a fluid control (e.g. a
syringe pump) interfaced with a needle tip, is positioned a
distance from a stage, 1102, comprising a plurality of projecting
lines, 1103. Both the stage and protruding lines comprise a
conductive material, and are electrically grounded, 1104, with the
needle tip. The protruding lines, 1103, have a vertical height,
1105, suitable for supporting a curved substrate, 1106. Flowing of
a nanowire precursor solution, 1107, results in disposition of
nanowires transverse, 1108, to the protruding lines, which align
the nanowires on the curved substrate, 1106. The stage, 1102, can
be rotated, 1109, as well as translated in the x-, y- and/or
z-directions, and/or tilted along axes .phi. and/or .theta..
Rotation and/or translation between disposing layers of nanowires
provides overlapping multi-layer nanowires coatings providing a
refractive index gradient.
[0261] In some embodiments, the disposing and/or aligning of
nanowires is performed using a stamp. As used herein, a "stamp"
refers to a three-dimensional object having a surface suitable for
adhering a nanowire thereto and transfer the nanowire to a
substrate. In some embodiments, a stamp comprises at least one
surface having a protrusion thereon that defines a pattern. Stamps
for use with the present invention are not particularly limited by
geometry, and can be flat, curved, smooth, rough, wavy, and
combinations thereof. In some embodiments, a stamp can have a three
dimensional shape suitable for conformally contacting at least a
portion of the stamp with a substrate.
[0262] In some embodiments, a stamp can comprise multiple surfaces
that can be flat or patterned, the latter embodiments comprising
the same or different patterns on multiple surfaces of a stamp. In
some embodiments, a stamp comprises a cylindrical surface
optionally including one or more protrusions on a curved surface of
the cylinder that define a pattern.
[0263] In some embodiments, a stamp comprises a flexible material.
As used herein, "flexible" refers to a material capable of being
flexed, or undergoing elastic or plastic deformation, bending,
compression, twisting, and the like in response to applied external
force, stress, strain and/or torsion. In some embodiments, a
flexible material is capable of being rolled upon itself. Preferred
flexible materials for use with a stamp of the present invention
include elastomeric polymers, i.e., "elastomers." Elastomers
suitable for use as a materials in a stamp include, but are not
limited to, a polyurethane, a resilin, an elastin, a polyimide, a
phenol formaldehyde polymer, a polydialkylsiloxane (e.g.,
polydimethylsiloxane, "PDMS"), a natural rubber, a polyisoprene, a
butyl rubber, a halogenated butyl rubber, a polybutadiene, a
styrene butadiene, a nitrile rubber, a hydrated nitrile rubber, a
chloroprene rubber (e.g., polychloroprene, available as
NEOPRENE.TM. and BAYPREN.RTM., Farbenfabriken Bayer AG Corp.,
Leverkusen-Bayerwerk, Germany), an ethylene propylene rubber, an
epichlorohydrin rubber, a polyacrylic rubber, a silicone rubber, a
fluorosilicone rubber, a fluoroelastomer (for example, those
described herein, supra), a perfluoroelastomer, a
tetrafluoroethylene/propylene rubber, a chlorosulfonated
polyethylene, an ethylene vinyl acetate, cross-linked variants
thereof, halogenated variants thereof, and combinations
thereof.
[0264] FIGS. 3A-3C provide three-dimensional schematic
representations, 300, 310 and 320, respectively, of stamps suitable
for use with the present invention. Referring to FIG. 3A, a stamp,
301, including a surface, 302, having a thickness, 303, is
provided. In some embodiments, a stamp comprises a backing layer,
304, including a back surface, 305, and a thickness, 306. A backing
layer can increase the dimensional stability of a stamp. In some
embodiments, a backing layer is rigid, semi-rigid, webbed,
multi-laminate, or a combination thereof. In some embodiments, a
backing layer has the same or a similar composition as a material
present in the stamp, but with a greater density.
[0265] Referring to FIG. 3B, a stamp, 311, including a surface,
312, having at least one protrusion thereon, 313, is provided. The
at least one protrusion, 313, includes a surface, 314. The surface
of a protrusion can be flat, curved (e.g., concave and/or convex),
pointed, and combinations thereof. The at least one protrusion has
lateral dimensions 315 (width) and 316 (length), and vertical
dimension 317 (height), each of which can be controlled
independently. The lateral dimensions of protrusions can be the
same or different across the surface of a stamp. The at least one
protrusion also includes a sidewall angle, 318, which refers to the
angle that the surface of the protrusion makes with the surface of
the stamp, 312. In some embodiments, a protrusion has a sidewall
angle of about .+-.50.degree., about .+-.40.degree., about
.+-.30.degree., about .+-.20.degree., about .+-.15.degree., about
.+-.10.degree., or about .+-.5.degree.. In some embodiments, a
pattern of protrusions on a stamp surface creates an array of
channels in a surface of a stamp, 319, the length and width of
which is defined by the protrusions on a stamp. In some
embodiments, the length and width of a channel on a stamp surface
is suitable for containing a nanowire.
[0266] In some embodiments, a stamp surface, 312, and/or a
protrusion surface, 314, can be functionalized and/or derivatized
to provide an adhesive or a repulsive interaction between a surface
and a nanowire. For example, in some embodiments, a surface of a
stamp can be functionalized to provide an adhesive interaction
between the surface and a nanowire, and a surface of a protrusion
can be functionalized (e.g., with a fluorinated moiety) to provide
a repulsive interaction between the surface and a nanowire.
[0267] In some embodiments, a substrate, a stamp surface, and/or a
protrusion on a stamp can be functionalized, derivatized, textured,
or otherwise pre-treated prior to disposing a nanowire or a polymer
composition thereon. As used herein, "pre-treating" refers to
chemically or physically modifying a surface. Pre-treating can
include, but is not limited to, cleaning, oxidizing, reducing,
derivatizing, functionalizing, exposing a surface to a reactive
gas, plasma, thermal energy, ultraviolet radiation, and
combinations thereof. Not being bound by any particular theory,
pre-treating a surface can increase or decrease an adhesive
interaction between a surface and a layer comprising a nanowire or
a polymer composition.
[0268] Referring to FIG. 1C, a stamp, 321, including a surface,
322, having at least one protrusion thereon, 323, is provided. The
at least one protrusion, 323, includes a surface, 324, that is
pointed. The at least one protrusion has lateral dimensions 325
(width) and 326 (length), and vertical dimension 327 (height), each
of which is controlled independently. The at least one protrusion
also includes a sidewall angle, 328.
[0269] In some embodiments, a layer of nanowires is deposited on a
substrate and the nanowires are aligned by contacting a stamp
having at least one protrusion thereon with the nanowires. For
example, a stamp having a surface including at least one protrusion
thereon forming a pattern of channels on the stamp surface can be
contacted with a substrate having nanowires thereon to align the
long axes of the nanowires in an orientation substantially parallel
to the channels of the stamp.
[0270] FIGS. 4A-4F provide three-dimensional schematic
cross-sectional representations of a process for providing an
anti-reflective surface of the present invention. Referring to FIG.
4A, a stamp, 401, having a surface, 402, is provided.
[0271] Nanowires are deposited onto the stamp surface, 410.
Referring to FIG. 4B, a stamp, 411, including a surface, 412,
having nanowires deposited thereon, 413, is provided. The nanowires
are aligned, 414, substantially parallel to one another. The
schematic representations of layers of nanowires having a thickness
corresponding to a single nanowire made herein are for purposes of
description and illustration only, and should be interpreted as
non-limiting.
[0272] In some embodiments, a layer of nanowires can be
co-deposited onto a stamp with a sacrificial material that can
facilitate deposition and/or alignment of the nanowires. Suitable
sacrificial materials include, but are not limited to, molecular
species, polymers, gels, sol-gels, dendrimers, oligomers, solvents,
and the like, and combinations thereof. In some embodiments, a
sacrificial material comprises an aliphatic or partially aliphatic
organic moiety that can be oxidized and/or volatized from a
substrate subsequent to the disposing.
[0273] In some embodiments, an electrospun layer of nanowires, is
deposited onto a stamp surface. The refractive index, density and
porosity of a nanowire layer can be controlled by the charge,
mass/charge ratio, and electric field strength used to prepare an
electrospun layer of nanowires (or nanofibers).
[0274] The nanowires are then contacted with a substrate, 420, to
deposit the nanowires on a substrate. Referring to FIG. 4C, a
stamp, 421, including a surface, 422, having nanowires deposited
thereon, 423, is contacted with a substrate, 431, having a surface,
432, to deposit the nanowires on the substrate. The stamp, 421, and
the substrate, 431, are aligned, 430, during the disposing. The
stamp is then removed from the substrate, 440.
[0275] Referring to FIG. 4D, a substrate, 441, including a surface,
442, having a layer, 444, of nanowires, 443, thereon is provided. A
second layer of nanowires is then deposited, 450, onto the first
layer of nanowires.
[0276] Referring to FIG. 4E, a stamp, 451, including a surface,
452, having nanowires deposited thereon, 453, is provided, and
contacted with a substrate, 461, including a surface, 462, having a
first layer, 464, of nanowires, 463, thereon, to deposit a second
layer of nanowires on the substrate. The stamp, 451, and the
substrate, 461, are aligned, 460, during the disposing. The stamp
is then removed from the substrate, 470.
[0277] Referring to FIG. 4F, a substrate, 471, including a surface,
472, having a first layer, 474, of nanowires, 473, and a second
layer, 476, of nanowires, 475, thereon is provided. The second
layer of nanowires, 476, has a refractive index that is less than a
refractive index of the first layer of nanowires, 474. The
nanowires comprising the first and second layers, 473 and 475,
respectively, can have a composition that is the same or different.
A third layer of nanowires is deposited on the second layer of
nanowires, 480, by repeating the process described herein, depicted
schematically in, e.g., FIGS. 4C and 4E.
[0278] The present invention is also directed to a process for
preparing an anti-reflective multi-layer coating on at least a
portion of a surface of a substrate, the process comprising:
[0279] printing on the surface a first laminar layer comprising a
first polymer and an optional second polymer;
[0280] disposing on the first laminar layer a second laminar layer
comprising the first polymer and the second polymer, wherein the
second laminar layer is substantially free from solvent, and the
second polymer is present in the second layer in a higher
concentration than the first layer;
[0281] printing on the second laminar layer a third laminar layer
comprising the first polymer and the second polymer, wherein the
third laminar layer is substantially free from solvent, and the
second polymer is present in the third layer in a higher
concentration than the second layer;
[0282] optionally exposing the first laminar layer to conditions
suitable for removing the second polymer from the first laminar
layer while retaining the first polymer within the first laminar
layer;
[0283] exposing the second laminar layer to conditions suitable for
removing the second polymer from the second laminar layer while
retaining the first polymer within the second laminar layer;
and
[0284] exposing the third laminar layer to conditions suitable for
removing the second polymer from the third laminar layer while
retaining the first polymer within the third laminar layer to
provide an anti-reflective multi-layer coating having a refractive
index gradient.
[0285] As used herein, "printing" refers to spatially controlled
deposition. While the deposition of polymer coatings is well known,
the formation of multi-layer polymer coatings having controlled
porosity has been difficult to achieve because solvents are
typically necessary to provide a uniform polymer deposition. The
present invention
[0286] In some embodiments, two or more polymers are dissolved in a
solvent and applied to a substrate (e.g., disposition of a first
layer on a substrate) or two or more polymers are dissolved in a
solvent and applied to a stamp, and the coated stamp is used to
print one or more layers on a substrate. As solvent is removed from
a deposited film comprising two or more polymers, the polymers are
selected such that phase separation occurs. The length scale of
phase separation can be controlled by the solvent (e.g., size,
polarity, functionality, rate of solvent removal, etc.) and can
vary from the millimeter length scale to the sub-nanometer length
scale. A solvent can be chosen that can dissolve only one of the
two polymers. One polymer is selected as the pore-forming moiety
and another polymer is a matrix forming moiety. The refractive
index of a resulting layer of a coating can be predetermined by the
refractive index of the matrix-forming polymer and the percentage
of the pore-forming polymer present in the composition.
[0287] Polymers suitable for use with the present invention include
matrix-forming polymers described herein. In some embodiments, a
polymer composition comprises polystyrene and polyvinylpyrrolidone
dissolved in a cyclohexane and/or ethanol. In some embodiments, a
polymer composition further comprises a sol-gel precursor such as
an alkoxysilane, a dialkoxysilane, a trialkoxysilane, a
tetraalkoxysilane, or a substituted variant thereof.
[0288] In some embodiments, printing comprises coating a stamp with
a polymer composition, and positioning the coated stamp surface
proximate to a substrate to transfer the polymer composition from
the stamp to the substrate.
[0289] In some embodiments, printing comprises:
[0290] coating an elastomeric stamp with a composition comprising a
pre-determined amount of the first polymer, the optional second
polymer, and a solvent to provide a coated stamp;
[0291] phase separating the polymers on the coated stamp;
[0292] removing the solvent from the composition; and
[0293] contacting the coated stamp with the surface under
conditions sufficient to transfer the composition from the coated
stamp to the surface.
[0294] A polymer composition can be applied to a stamp surface by a
coating method known in the art such as, but not limited to, screen
printing, ink jet printing, syringe deposition, spraying, spin
coating, brushing, atomizing, dipping, aerosol depositing,
capillary wicking, and combinations thereof. In some embodiments,
applying a resist composition to a stamp surface comprises spin
coating (i.e., rotating the stamp surface at about 100 revolutions
per minute (rpm) to about 5,000 rpm while pouring or spraying the
resist composition onto the stamp surface).
[0295] In some embodiments, a polymer composition is dissolved in a
solvent to facilitate uniform coating of a stamp surface. Solvents
suitable for dissolving a polymer composition for application to a
stamp include, but are not limited to, C.sub.6-C.sub.15 straight
chain, branched and cyclic hydrocarbons (e.g., hexane, cyclohexane
and the like), C.sub.6-C.sub.16 aryl and aralkyl hydrocarbons
(e.g., benzene, toluene, xylene, and the like), C.sub.1-C.sub.15
alkyl, aryl, and aralkyl alcohols (e.g., methanol, ethanol,
propanol, butanol, and the like), C.sub.6-C.sub.15 alkyl, aryl, and
aralkyl amines, C.sub.6-C.sub.15 alkyl, aryl, and aralkyl amides
(e.g., dimethylformamide, N-methylpyrrolidone, and the like),
C.sub.6-C.sub.15 alkyl and aralkyl ketones (e.g., acetone,
methylethylketone, benzophenone, and the like), C.sub.6-C.sub.15
esters (e.g., ethyl acetate and the like), C.sub.6-C.sub.15 alkyl
and aralkyl ethers (e.g., ethyleneglycol dimethylether and the
like), and combinations thereof.
[0296] In some embodiments, a solvent is chosen from: benzene,
toluene, a xylene, cumene, mesitylene, propylene glycol mono-methyl
ether, tetrahydrofuran, dodecane, tetralin, pyridine,
tetrahydrofuran, acetone, ethylacetate, methylethylketone,
methylene chloride, 1,2-dichloroethane, chloroform, chlorobenzene,
dimethylformamide, and combinations thereof.
[0297] Exposing can comprise a process such as, but not limited to,
heating a laminar layer, irradiating a laminar layer with
electromagnetic radiation, irradiating a laminar layer with an
electron beam, exposing to a selective solvent, pyrrolizing a
laminar layer, exposing a laminar layer to a plasma, and
combinations thereof. The conditions of the exposing are selected
such that a matrix-forming polymer is not removed from a coating
layer, while a pore-forming polymer is volatized to create a porous
matrix. The refractive index of the layer is therefore dependent
upon the degree of porosity in the resulting matrix, as well as the
refractive index of the matrix-forming polymer. In some
embodiments, exposing comprises exposing to a selective solvent
(i.e., a solvent that is selective for dissolving a pore-forming
moiety and/or polymer).
[0298] In some embodiments, the optionally exposing is performed
simultaneous with the exposing the second laminar layer and the
exposing the third laminar layer. Thus, the present invention
includes introducing porosity into the layers of a multi-layer
coating in serial or simultaneously.
[0299] In some embodiments, the optionally exposing is performed
prior to the printing on the first laminar layer a second laminar
layer; and the exposing the second laminar layer is performed prior
to printing on the second laminar layer a third laminar layer.
[0300] In some embodiments, the present invention further comprises
cross-linking at least one of the polymers present in a polymer
composition. Cross-linking can include intramolecular
cross-linking, intermolecular cross-linking, the addition of a
molecular cross-linker into one or more of the layers of a
multi-layer coating, and combinations thereof.
[0301] In some embodiments, a process further comprises
post-treating a multi-layer coating to increase the mechanical
strength of the coating, increase an adhesive interaction between
the coating and a substrate, increase an interlayer adhesive
interaction, enhance the chemical stability of a coating, enhance
the density of a coating layer, and combinations thereof.
Post-treating processes include, without limitation, annealing,
calcining, sintering, exposing to ultraviolet light, exposing to
plasma, and combinations thereof. Post-treating can be performed in
a serial manner (e.g., after a deposition and exposing process), a
semi-serial manner (e.g., after a deposition of every 2-3 layers of
a multi-layer coating), or as a single post-treatment process after
deposition of a multi-layer coating.
[0302] Unlike spin-coating, spray coating, and chemical vapor
deposition, the solvent-less disposing (e.g., stamping) of the
present invention can deposit multi-layer coatings without
modification or damage to underlying layers of a coating during the
later deposition processes. For example, multi-layer coatings
cannot be easily deposited by spin-coating without the
later-deposited coating layers dissolving underlying layers of the
coating.
[0303] The tensile strength and/or chemical functionality of the
coatings of the present invention can be modified by, for example,
functionalizing the nanowires, modifying the surfaces of the
coatings and/or annealing the coatings.
[0304] In some embodiments, the process of the present invention
further comprises polishing a roughened surface of a coating. Not
being bound by any particular theory, surface roughness on the
order of about 100 nm to about 100 .mu.m can improve the smudge
resistance of a coating. However, a roughened surface will
typically exhibit decreased optical transmission properties
compared with a smooth surface of the same composition. In some
embodiments, the optical transmission of a roughened surface can be
improved by polishing. Roughened surfaces of the present invention
can be polished by a process selected from: chemically polishing,
mechanically polishing, thermally polishing, and combinations
thereof.
[0305] As used herein, "chemically polishing" refers to a process
of applying an acidic reagent, a basic reagent, a fluoride reagent,
or a combination thereof to a surface, whereby reaction between the
surface and a reagent reduces the frequency of sub-100 nm features
on the surface.
[0306] Acidic reagents suitable for use with the present invention
include, but are not limited to, sulfuric acid,
trifluoromethanesulfonic acid, fluorosulfonic acid, trifluoroacetic
acid, hydrofluoric acid, hydrochloric acid, carborane acid, and
combinations thereof.
[0307] Basic reagents suitable for use with the present invention
include, but are not limited to, sodium hydroxide, potassium
hydroxide, ammonium hydroxide, tetraalkylammonium hydroxide
ammonia, ethanolamine, ethylenediamine, and combinations
thereof.
[0308] Fluoride reagents suitable for use with the present
invention include, but are not limited to, elemental fluorine,
ammonium fluoride, lithium fluoride, sodium fluoride, potassium
fluoride, rubidium fluoride, cesium fluoride, francium fluoride,
antimony fluoride, calcium fluoride, ammonium tetrafluoroborate,
potassium tetrafluoroborate, and combinations thereof.
[0309] As used herein, "mechanically polishing" refers to processes
selected from: contacting a particulate composition with a surface,
brushing a surface, and combinations thereof, whereby friction
and/or mechanical interaction with a surface reduces the frequency
of sub-100 nm features on the surface.
[0310] As used herein, "thermally polishing" refers to a process of
applying thermal energy to a surface, whereby the thermal energy
reduces the frequency of sub-100 nm features on the surface. In
some embodiments, a thermal energy is chosen from: a convective
thermal energy (e.g., heating in an oven or furnace), a conductive
thermal energy (contacting the substrate or film with a heating
element and the like), an electromagnetic thermal energy (e.g.,
infrared light), a plasma thermal energy (e.g., a plasma at about
50.degree. C. or greater), and combinations thereof.
EXAMPLES
Hypothetical Example 1
[0311] An unpatterned (flat) 200 mm by 200 mm square-shaped stamp
comprising a flexible material (polydimethylsiloxane, "PDMS") can
be prepared by coating a flat master (e.g., silicon) using methods
previously described elsewhere. See, e.g., U.S. Pat. Nos. 5,512,131
and 5,900,160, which are incorporated herein by reference in their
entirety. The stamp can be spin-coated with a thin layer of a
polymer composition (90 wt-% polystyrene and 10 wt-%
polyvinylpyrrolidone) dissolved in a solvent (a 1:1 ethanol and
toluene, v/v), 4% polymer by weight. The polymer-coated stamp can
be dried to remove the solvent and then contacted for about 60
seconds with a substrate. The substrate can be heated (at about
80.degree. C. to about 130.degree. C.) during the contacting to
promote transfer of the polymer from the stamp to the
substrate.
[0312] The above process can be repeated using a second polymer
composition (80 wt-% polystyrene and 20 wt-% polyvinylpyrrolidone)
to provide a second polymer layer. Similarly, a third polymer layer
can be deposited using a third polymer composition (70 wt-%
polystyrene and 30 wt-% polyvinylpyrrolidone).
[0313] The polyvinylpyrrolidone can then be removed from the
multi-layer coating by exposing the multi-layer coating to ethanol.
The resulting multi-layer, refractive index gradient coating can be
optionally annealed to stabilize its chemical composition.
Hypothetical Example 2
[0314] In another embodiment, the composite film prepared in
Hypothetical Example 1 can be post-treated to increase the
hydrophobicity of the surface of the coating. For example, the
coating can be exposed to a vapor comprising
tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane to
functionalize the top surface of the coating.
Example 3
[0315] Aligned layers of composite nanowires (i.e., nanofibers
comprising zinc acetate and polyvinylpyrrolidone, 1:1 by weight,
"ZnAc-PVP nanowires") were electrospun from a precursor solution of
3:3:20:10 parts by weight zinc
acetate:polyvinylpyrrolidone:ethanol:water. The layers of ZnAc-PVP
nanowires were deposited by flowing the precursor solution at a
flow rate of 0.206 mL/hr to 0.274 mL/hr through a needle having a
21-24 gauge diameter and to which was applied a DC voltage of 17-20
kV. The flow rate of the precursor solution was controlled using a
syringe pump. A collector (two electrically grounded metal blades
having a separation distance of about 13 mm) was placed about 20 cm
from the needle tip. Uniaxially aligned composite ZnAc-PVP
nanowires were collected using the collector and transferred from
the collector to a silicon substrate by passing the substrate
through the array of uniaxially aligned ZnAc-PVP nanowires. Many of
the ZnAc-PVP nanowires had a length of 13 mm or more and a diameter
of about 1-5 .mu.m. Three dimensional coatings of layered ZnAc-PVP
nanowires were produced by rotating the substrate about 90.degree.
between passes through the collected ZnAc-PVP nanowires. This
resulted in four layers being deposited with the ZnAc-PVP nanowires
in each layer being substantially orthogonal to those ZnAc-PVP
nanowires in adjoining (i.e., adjacent) layers.
[0316] An optical image of the deposited four layer ZnAc-PVP
nanowire coating is provided in FIG. 5. Referring to FIG. 5, the
image, 500, at 5.times. resolution shows overlapping ZnAc-PVP
nanowires on a silicon substrate.
Example 4
[0317] The composite ZnAc-PVP nanowire coating prepared in Example
3 was converted to a ZnO nanowire coating by heating the composite
coating and substrate to 550.degree. C. at a ramp rate of about
2.degree. C. per minute, holding at 550.degree. C. for about 13
hours, and then cooling the calcined coating to room temperature
(about 21.degree. C.) over about 4 hours to provide a multi-layer
coating of ZnO nanowires.
[0318] In general, the composite ZnAc-PVP nanowires can be
converted to ZnO nanowires by calcination and sintering at about
450.degree. C. to about 550.degree. C. for about 1 hour to about 15
hours.
[0319] An optical image of the four layer ZnO nanowire coating is
provided in FIG. 6. Referring to FIG. 6, the image, 600, at
100.times. resolution shows overlapping ZnAc-PVP nanowires, 601, on
a silicon substrate, 602.
Hypothetical Example 5
[0320] In another embodiment the ZnO nanowire multi-layer coating
prepared in Example 4 can be converted to provide a multi-layer
coating of ZnS nanowires by annealing the substrate and ZnO
nanowire multi-layer coating in a H.sub.2S atmosphere at about
500.degree. C. to about 550.degree. C. for about 1 hour to about 10
hours.
Hypothetical Example 6
[0321] An unpatterned (flat) 4 cm by 4 cm stamp comprising a
flexible material (polydimethylsiloxane, "PDMS") can be prepared as
in Hypothetical Example 1. A first solution and/or suspension of
nanowires can be spin-coated onto the flexible stamp. A second
flexible stamp can be contacted with the surface of the flexible
stamp bearing the nanowires, and can then be gently pressed and
dragged across the surface of the first flexible stamp for a
distance of about 3 mm. The shear forces induced by the contact and
motion can align the nanowires on the surface of the first flexible
stamp as to provide a single, dense layer of nanowires on the
surface of the first flexible stamp. The aligned layer of nanowires
can then be transferred to a substrate by contacting at least the
aligned layer of nanowires with a substrate. A portion of the
surface of the flexible stamp can also contact in the substrate
during the transferring.
[0322] This process (i.e., disposing a solution of nanowires on a
flexible stamp and aligning the nanowires) can then be repeated
using a second solution and/or suspension of nanowires, wherein the
second solution and/or suspension of nanowires can have a nanowire
concentration less than the first solution and/or suspension (e.g.,
the second solution can have a concentration of nanowires about 25%
less than the concentration of the first solution). An aligned
layer of nanowires prepared from the second solution can then be
transferred to the substrate comprising the first aligned layer of
nanowires. The substrate can be rotated about 90.degree. to provide
a second layer of aligned nanowires on top of and substantially
perpendicular to the first layer of aligned nanowires. A third
layer of nanowires can be prepared in a similar manner, wherein a
third solution and/or suspension of nanowires can have a
concentration of nanowires that is about 50% less than the first
solution. After disposing and aligning the nanowires on a flexible
stamp, the third aligned layer of nanowires can be transferred to
the substrate and oriented substantially perpendicular to the
second aligned layer of nanowires. Optionally, a fourth layer of
nanowires can be prepared in a similar manner, wherein a fourth
solution and/or suspension of nanowires can have a concentration of
nanowires that is about 75% less than the first solution. After
disposing and aligning the nanowires on a flexible stamp, the
fourth aligned layer of nanowires can be transferred to the
substrate and oriented substantially perpendicular to the third
aligned layer of nanowires. The resulting multi-layer nanowire
coating can be sintered to anneal the nanowire layers to each
other, as well as providing increased adhesion of the nanowire
coating to the substrate.
Example 7
[0323] Aligned layers of composite nanowires (zinc
acetate:polyvinylpyrrolidone nanowires, 1:1 by weight, "ZnAc-PVP
nanowires") were deposited from a precursor solution of 3:3:20:10
parts by weight zinc acetate:polyvinylpyrrolidone:ethanol:water
onto a substrate (e.g., a 20 mm by 20 mm square substrate). The
layers of ZnAc-PVP nanowires were deposited by flowing the
precursor solution at a flow rate of 0.206 mL/hr to 0.274 mL/hr
through a needle having a 21-24 gauge diameter, to which was
applied a DC voltage of 17-20 kV. The flow rate of the precursor
solution was controlled using a syringe pump. A collector (two
electrically grounded metal blades having a separation distance of
about 25 mm) was placed about 20 cm from the needle tip with the
substrate placed between the grounded blades about 20 cm from the
needle tip, wherein the substrate surface was oriented normal to
the needle tip.
[0324] FIGS. 7A and 7B provide a top-view schematic representation
of this arrangement and a method of aligned nanowire deposition
using this arrangement. Referring to FIG. 7A, a substrate, 701, is
positioned between grounded metal blades (e.g., electrodes) and
nanowires can be directly deposited on the substrate, 704. An
optional second set of ungrounded metal blades, 703, orthogonal to
the first set of metal blades is also depicted. Uniaxially aligned
composite nanowires (e.g., ZnAc-PVP nanowires) were collected
directly on the substrate until a desirable density of nanowires
was obtained. A second layer of nanowires was then deposited onto
the first layer of nanowires, 709.
[0325] Referring to FIG. 7B, three dimensional coatings of layered
nanowires can be produced by grounding the second set of metal
blades, 713, and flowing the precursor as described above.
Alternatively, the second layer of nanowires, 715, can be deposited
by first rotating the substrate, 711, about 90.degree. between the
first set of grounded metal blades, 712. Thus, a second layer of
aligned nanowires, 715, can be deposited directly onto the first
layer of aligned nanowires, 714. Repeating this process (i.e.,
rotating or grounding alternating pairs of metal blades and then
disposing) can permit multi-layer nanowire coatings having a
tunable density to be deposited, wherein nanowires in adjacent
layers are substantially orthogonal to one another.
[0326] The ZnAc-PVP nanowires were optionally calcined as described
in Example 4 to provide a multi-layer coating comprising ZnO
nanowires. ZnS nanowires can subsequently be optionally chemically
treated, as described in Hypothetical Example 5 to provide a
multi-layer coating of ZnS nanowires.
Example 8
[0327] The density of ZnO nanowires in a layer, as deposited by the
process described in Example 7, can be controlled by varying the
deposition time. Zn-PVP nanowires were deposited on sapphire
substrates according to the process of Example 7 followed by
calcination at 550.degree. C. for a period of about 1 hour to about
15 hours. The density of the ZnO nanowires was determined using
optical microscopy by counting the number of nanowires per linear
micrometer of the substrate, the results of which are provided in
the following Table.
TABLE-US-00001 TABLE ZnO nanowire density per unit length of
substrate as a function of deposition time, and nanowire density
per second. Each data point is an average of 3 depositions imaged
at a minimum of three locations per sample using a Scanning
Electron Microscope. Deposition Time ZnO Nanowire Density ZnO
Density/Time (minutes) (NW/.mu.m) (NW/.mu.m s.sup.-1) 0.5 0.2 .+-.
0.1 0.007 .+-. 0.003 1 0.5 .+-. 0.05 0.008 .+-. 0.001 2 0.8 .+-.
0.25 0.007 .+-. 0.002 5 1.5 .+-. 0.35 0.005 .+-. 0.001 10 2.3 .+-.
0.95 0.004 .+-. 0.001
[0328] As shown in the above Table, for deposition times up to
about 2 minutes, there is a linear relationship between deposition
time and nanowire density. This can also be seen as a constant
nanowire density as a function of deposition time of 0.007-0.008
nanowires per micron per second for deposition times of about two
minutes or less. However, for deposition times of 5 and 10 minutes,
the density of ZnO nanowires per unit time began to decrease to
about 0.004-0.005 nanowires per micron per second. This resulted in
an overall non-linear relationship between ZnO nanowire density as
a function of deposition time (for deposition times of 30 seconds
to 10 minutes).
[0329] The data for ZnO nanowire density as a function of
deposition time are consistent with the results for other nanowire
materials deposited by electrospinning.
[0330] Not being bound by any particular theory, the nanowires that
collect on the grounded plates can discharge static charge present
on the surface of the nanowires. However, nanowires that are
deposited on the substrate present between the grounded plates
remain charged. This latent charge on the nanowires affects newly
deposited nanowires deposited across the grounded plates, and can
assist with nanowire alignment, but may also potentially limit the
density of nanowires deposited in highly dense layers. Another
factor that can determine the maximum surface density of nanowires
within a single layer is the degree to which nanowires are aligned
relative to one another, as misaligned nanowires can increase the
volume of a layer but not necessarily result in an increased
surface density of nanowires on the substrate. The effect of latent
charge on the density of deposited nanowires can be diminished by
removing static charge from the deposited nanowires periodically
during the deposition process.
[0331] Using the process parameters of Example 7, gradient
refractive index ("GRIN") coatings comprising 5 layers of ZnO
nanowires, wherein a first layer of ZnO nanowires was deposited for
10 minutes, followed by a second layer of ZnO nanowires deposited
for 5 minutes, a third layer that was deposited for 2 minutes, a
fourth layer that was deposited for 1 minute, and a fifth layer
that was deposited for 30 seconds, and wherein after each
deposition, the substrate was rotated about 90.degree..
Example 9A
[0332] ZrO.sub.2 nanowire-containing coatings comprising 5 layers
of aligned composite nanowires (zirconium
oxide:polyvinylpyrrolidone nanowires, "ZrO.sub.2-PVP nanowires")
were deposited from a precursor solution using the following
process conditions to provide a coating containing ZrO.sub.2-PVP
nanowires having an average diameter of about 175 nm.
[0333] ZrO.sub.2-PVP nanowires having an average diameter of about
175 nm were prepared from a precursor solution comprising 70%
zirconium propoxide in n-propanol (5 g), polyvinylpyrrolidone (750
mg), and ethanol (4.25 g). The precursor solution was flowed (0.19
mL/hr) through a 25 gauge needle to which was applied a DC voltage
of about 8 kV to about 11 kV.
[0334] A collector (two electrically grounded metal blades having a
separation distance of about 25 mm) was placed about 20 cm from the
needle tip with the substrate placed between the grounded blades
about 20 cm from the needle tip, wherein the substrate surface was
oriented normal to the needle tip. The relative humidity was
maintained at less than about 40% during the deposition of the
nanowires.
[0335] A first layer of nanowires was deposited for 10 minutes,
followed by a second layer of nanowires deposited for 5 minutes, a
third layer that was deposited for 2 minutes, a fourth layer that
was deposited for 1 minute, and a fifth layer that was deposited
for 30 seconds. After each deposition, the substrate was rotated
90.degree..
[0336] Using these process parameters, single layers of aligned
ZrO.sub.2 nanowires were deposited on various substrates, as well
as gradient refractive index ("GRIN") coatings comprising 5 layers
of ZrO.sub.2 nanowires, wherein a first layer of ZrO.sub.2
nanowires was deposited for 10 minutes, followed by a second layer
of ZrO.sub.2 nanowires deposited for 5 minutes, a third layer that
was deposited for 2 minutes, a fourth layer that was deposited for
1 minute, and a fifth layer that was deposited for 30 seconds, and
wherein after each deposition, the substrate was rotated about
90.degree..
Example 9B
[0337] ZrO.sub.2-PVP nanowires having an average diameter of about
500 nm were prepared as described in Example 9A, except that a
precursor solution comprising 70% zirconium propoxide in n-propanol
(1.42 mL), polyvinylpyrrolidone (1050 mg), and ethanol (7.45 g) was
used. The precursor solution was flowed (0.4 mL/hr) through a 25
gauge needle to which was applied a DC voltage of about 10 kV to
about 12 kV. The flow rate of the precursor solution was controlled
using a syringe pump.
[0338] Using these process parameters, single layers of aligned
ZrO.sub.2 nanowires were deposited on various substrates, as well
as gradient refractive index ("GRIN") coatings comprising 5 layers
of ZrO.sub.2 nanowires, wherein a first layer of ZrO.sub.2
nanowires was deposited for 10 minutes, followed by a second layer
of ZrO.sub.2 nanowires deposited for 5 minutes, a third layer that
was deposited for 2 minutes, a fourth layer that was deposited for
1 minute, and a fifth layer that was deposited for 30 seconds, and
wherein after each deposition, the substrate was rotated about
90.degree..
Example 10
[0339] Titania-PVP (TiO.sub.x-PVP) nanowires were prepared by
combining a first solution containing polyvinylpyrrolidone (250 mg)
in ethanol (2.75 mL) with a second solution containing titanium
isopropoxide (250 mg) in ethanol (1 mL) and glacial acetic acid (1
mL). The resulting solution was mixed for about 12 h or longer
until a clear yellow to orange solution resulted.
[0340] TiO.sub.x-PVP nanowires having an average diameter of about
100 nm or less were prepared by flowing the precursor solution
(0.12 mL/hr) through a 27 gauge needle to which was applied a DC
voltage of 7-10 kV. The flow rate of the precursor solution was
controlled using a syringe pump. A collector (two electrically
grounded metal blades having a separation distance of about 25 mm)
was placed about 20 cm from the needle tip with the substrate
placed between the grounded blades about 20 cm from the needle tip,
wherein the substrate surface was oriented normal to the needle
tip. The relative humidity was maintained at about 25% to about 35%
during the depositing. The relative humidity was maintained at less
than about 40% during the deposition of the nanowires.
[0341] Using these process parameters, single layers of aligned
TiO.sub.2 nanowires were deposited on various substrates, as well
as gradient refractive index ("GRIN") coatings comprising 5 layers
of TiO.sub.2 nanowires, wherein a first layer of TiO.sub.2
nanowires was deposited for 10 minutes, followed by a second layer
of TiO.sub.2 nanowires deposited for minutes, a third layer that
was deposited for 2 minutes, a fourth layer that was deposited for
1 minute, and a fifth layer that was deposited for 30 seconds, and
wherein after each deposition, the substrate was rotated about
90.degree..
Example 11
[0342] Alumina-PVP (AlO.sub.x-PVP) nanowires were prepared by
combining a first solution containing polyvinylpyrrolidone (250 mg)
in ethanol (2.75 mL) with a second solution containing aluminum
isopropoxide (250 mg) in iso-propanol (1 mL) and glacial acetic
acid (1 mL). Prior to combining, the second solution was typically
sonicated and vortex mixed until the aluminum isopropoxide was
completely dissolved (i.e., the solution was clear and colorless).
The resulting precursor solution was also clear and colorless or
clear with a slightly gray color.
[0343] AlO.sub.x-PVP nanowires having an average diameter of about
100 nm or less were prepared by flowing the precursor solution
(0.09 mL/hr) through a 27 gauge needle to which was applied a DC
voltage of 7-10 kV. The flow rate of the precursor solution was
controlled using a syringe pump. A collector (two electrically
grounded metal blades having a separation distance of about 25 mm)
was placed about 20 cm from the needle tip with the substrate
placed between the grounded blades about 20 cm from the needle tip,
wherein the substrate surface was oriented normal to the needle
tip. The relative humidity was maintained at less than about 40%
during the deposition of the nanowires.
[0344] Using these process parameters, single layers of aligned
Al.sub.2O.sub.3 nanowires were deposited on various substrates, as
well as gradient refractive index ("GRIN") coatings comprising 5
layers of Al.sub.2O.sub.3 nanowires, wherein a first layer of
Al.sub.2O.sub.3 nanowires was deposited for 10 minutes, followed by
a second layer of Al.sub.2O.sub.3 nanowires deposited for 5
minutes, a third layer that was deposited for 2 minutes, a fourth
layer that was deposited for 1 minute, and a fifth layer that was
deposited for 30 seconds, and wherein after each deposition, the
substrate was rotated about 90.degree..
Example 12
[0345] The ZrO.sub.2-PVP, TiO.sub.x-PVP and AlO.sub.x-PVP nanowire
coatings prepared in Examples 9B, 10 and 11, respectively, were
calcined at 550.degree. C., 750.degree. C., or 950.degree. C., and
then cooled to room temperature to provide a multi-layer coating
metal oxide nanowire coatings. The nanowire coatings were then
removed from the substrates, pulverized, and the structure of the
materials was characterized using x-ray powder diffraction. The
pulverized samples were applied to a zero-background holder and
placed in a PANALYTICAL.RTM. X'Pert Pro Deffractometer (PANalytical
B.V., Almelo, NL) and irradiated with 45 kV/40 mA radiation from a
Cu source. Data was acquired over a range of 10.degree. to
70.degree. with a step size of 0.0158.degree. and a counting time
of 500 seconds per step. After diffraction patterns were acquired,
phases were determined using Rietveld refinement, or with the aid
of the Powder Diffraction File published by the International
Centre for Diffraction Data. As shown in the following Table, the
calcination temperature was found to significantly affect the
structure of the resulting metal oxide nanowires.
TABLE-US-00002 TABLE Nanowire structure as a function of
calcination temperature, as determined by powder x-ray diffraction.
Calcination Temperature Material 550.degree. C. 750.degree. C.
950.degree. C. Zirconia amorphous amorphous with 100% .gamma.-Al2O3
(Example 9B) trace .gamma.-Al2O3 Titania 86% anatase; 6% anatase;
100% rutile (Example 10) 14% rutile 94% rutile Alumina 100%
tetragonal 18% tetragonal; 3% tetragonal; (Example 11) 82%
monoclinic 97% monoclinic
Example 13
[0346] GeO-PVP (GeO-PVAC) nanowires were prepared by combining a
first solution containing polyvinylacetate (230 mg) in acetone
(1.79 mL) with a second solution containing
tetra-iso-propoxygermane (0.244 mL) in iso-propanol (1 mL),
propionic acid (0.123 mL), and water (0.031 mL). The precursor
solution was used immediately after mixing by flowing the precursor
solution (0.4 mL/hr) through a 27 gauge needle to which was applied
a DC voltage of 11-12 kV. The flow rate of the precursor solution
was controlled using a syringe pump. A collector (two electrically
grounded metal blades having a separation distance of about 25 mm)
was placed about 20 cm from the needle tip with the substrate
placed between the grounded blades about 20 cm from the needle tip,
wherein the substrate surface was oriented normal to the needle
tip. The relative humidity was maintained at less than about 40%
during the deposition of the nanowires.
[0347] The GeO-PVP nanowires were calcined in air at a temperature
of about 550.degree. C. to provide germanium oxide nanowires.
Scanning Auger microanalysis of the germanium oxide nanowires
indicate a Ge:O stoichiometry of about 1:1 (i.e., GeO).
[0348] Using these process parameters, single layers of aligned GeO
nanowires were deposited on various substrates, as well as gradient
refractive index ("GRIN") coatings comprising 5 layers of GeO
nanowires, wherein a first layer of GeO nanowires was deposited for
10 minutes, followed by a second layer of GeO nanowires deposited
for 5 minutes, a third layer that was deposited for 2 minutes, a
fourth layer that was deposited for 1 minute, and a fifth layer
that was deposited for 30 seconds, and wherein after each
deposition, the substrate was rotated about 90.degree..
Example 14
[0349] Aligned carbon (C) nanowires were prepared by mixing
polyacrylonitrile (PAN) in dimethylformamide (DMF) to provide a 10%
by weight mixture of PAN in DMF. The mixture heated in a water bath
(.about.70.degree. C.) until a clear, colorless precursor solution
resulted. The precursor solution was flowed (0.1 mL/hr) through a
21 gauge needle to which was applied a DC voltage of 5-7 kV. The
flow rate of the precursor solution was controlled using a syringe
pump. A collector (two electrically grounded metal blades having a
separation distance of about 25 mm) was placed about 20 cm from the
needle tip with the substrate placed between the grounded blades
about 20 cm from the needle tip, wherein the substrate surface was
oriented normal to the needle tip. The relative humidity was
maintained at less than about 40% during the deposition of the
nanowires.
[0350] The C nanowires were immediately placed in a 270.degree. C.
furnace for 15 minutes to stabilize the nanowires. After
stabilization, the C nanowires were heated in an inert (Ar)
atmosphere to a temperature of about 1100.degree. C. for one hour
with a ramp rate of 10.degree. C./minute.
[0351] Using these process parameters, single layers of aligned C
nanowires were deposited on various substrates, as well as gradient
refractive index ("GRIN") coatings comprising 5 layers of C
nanowires, wherein a first layer of C nanowires was deposited for
10 minutes, followed by a second layer of C nanowires deposited for
5 minutes, a third layer that was deposited for 2 minutes, a fourth
layer that was deposited for 1 minute, and a fifth layer that was
deposited for 30 seconds, and wherein after each deposition, the
substrate was rotated about 90.degree..
Example 15A
[0352] An ZrO.sub.2 nanowire coating was deposited on a circular
ZnS substrate (1'' diameter) by flowing a precursor solution
comprising 70% zirconium propoxide in n-propanol (1.42 mL),
polyvinylpyrrolidone (1050 mg), and ethanol (7.45 g). The precursor
solution was flowed (0.4 mL/hr) through a 25 gauge needle to which
was applied a DC voltage of about 10 kV to about 12 kV. The flow
rate of the precursor solution was controlled using a syringe
pump.
[0353] A collector comprising an two negatively biased aluminum
plates (5 kV) was placed about 15 cm from the needle tip. The
substrate was placed between the plates at a distance about 1 mm or
less, closer to the needle tip compared to the collector plates.
The ZrO.sub.2-PVP composite nanowires were collected for across the
substrate on the biased metal plates when the precursor solution
was flowed. The depositing (i.e., electrospinning and collecting)
was performed for 10 minutes in a humidity-controlled environment
having a relative humidity of about 40% or less.
[0354] The ZrO.sub.2-PVP wires were transferred from the collector
to a ZnS substrate that was placed in a furnace pre-heated to
200.degree. C. The furnace was then ramped to 550.degree. C. at a
rate of about 2.degree. C. to about 10.degree. C. per minute, and
then the furnace temperature was held at 500.degree. C. for 1 hour.
The ZrO.sub.2 nanowires had an average diameter of about 500 nm,
and the layer of ZrO.sub.2 nanowires had a thickness of about 1.5
.mu.m to about 2 .mu.m.
[0355] The anti-reflective properties of the ZrO.sub.2 nanowire
coating was determined qualitatively by comparing the reflection
from the nanowire-coated ZnS substrate with an uncoated ZnS
substrate. The results are depicted in FIG. 8. Referring to FIG. 8,
a photographic image, 800, shows an uncoated ZnS substrate, 801,
alongside the ZrO.sub.2 nanowire-coated ZnS substrate, 811, which
are resting on a sheet of paper having printing thereon. The
uncoated ZnS substrate, 801, has significant glare, 802, and it is
difficult to read the printing, 803, on the sheet of paper beneath
the substrate. Conversely, the printing on the sheet of paper, 813,
underneath the ZrO2-nanowire-coated ZnS substrate is readily viewed
without glare or other interference.
Example 15B
[0356] A ZnS substrate having a ZrO.sub.2 nanowire coating thereon
(as prepared in Example 15A) was coated with a
styrene-ethylene-butylene triblock co-polymer having maleic
anhydride groups grafted thereto ("SEBMA"). A solution of the SEBMA
polymer in toluene (2% w/v) was applied to the ZnS substrate using
a syringe (about 3-5 mL). The excess solution was allowed to drain
from the substrate, and the coated substrate was dried in a
chemical fume hood for about 5 min, and then placed in a heated
furnace for about 2 minutes at about 130.degree. C. The polymer
coating thickness was about 200 nm on the substrate, and also
coated the nanowires in a thin polymeric layer.
Example 15C
[0357] The transmittance of the coated ZnS substrates was
determined in the visible and near-IR regions of the spectrum.
Between 350 nm and 1.1 .mu.m, a JASCO.RTM. V630 UV-Vis
spectrophotometer (Jasco Corp., Tokyo, JP) was utilized to
determine the percent transmittance of the samples, whereas between
2.5 .mu.m and 14 .mu.m, a JASCO.RTM. V4100 FT-IR spectrophotometer
(Jasco Corp., Tokyo, JP) was utilized to determine the percent
transmittance of the samples. The results are reported in the
following Table. Each entry in the Table below is an average of 10
samples.
TABLE-US-00003 TABLE Percent transmittance (% T) for uncoated ZnS,
and ZnS substrates having a ZrO.sub.2 nanowire coating thereon. % T
as a function of Wavelength Sample 1.06 .mu.m 2.5 .mu.m 8-10 .mu.m
ZnS (uncoated) 66% .+-. 1 81% .+-. 1 81% .+-. 1 ZrO.sub.2
nanowire-coated ZnS 61% .+-. 10 83% .+-. 5 82% .+-. 2 (Example 15A)
ZrO.sub.2 nanowires encapsulated on ZnS 53% .+-. 15 88% .+-. 5 83%
.+-. 2 (Example 15B)
[0358] The ZrO.sub.2 nanowire-coated ZnS substrate (Example 13A)
increased the transmittance at 2.5 .mu.m from 81% to 83%, while the
encapsulated ZrO.sub.2 nanowire-coated ZnS substrate increased the
transmittance to 88% at 2.5 .mu.m. In the 8-10 .mu.m region the
improvement in transmission was 1% to 2%. At the shorter wavelength
(1.06 .mu.m) the nanowire coatings caused a decrease of 5% and 13%,
respectively, in the percent transmittance. However, several of the
samples exhibited greater than 65% transmittance at 1.06 .mu.m,
suggesting that the nanowire coatings can be optimized to provide
the required transmittance at the target wavelength.
[0359] Not being bound by any particular theory, the decrease in
transmittance in the near-IR region of the spectrum (i.e., at 1.06
.mu.m) for the ZrO.sub.2 nanowire-coated ZnS substrates was due in
part to the large diameter of the ZrO.sub.2 nanowires present in
the coatings, which was approximately 500 nm.
Example 16
[0360] TiO.sub.x-PVP nanowire- and AlO.sub.x-PVP nanowire-coated
ZnS substrates were prepared by the deposition methods described in
Examples 11 and 12, respectively, followed by calcination at
550.degree. C. (as described in Example 13). Encapsulated
nanowire-coated samples were also prepared using the procedure
described in Example 15B. The average diameter of the nanowires
used in each sample was less than 100 nm.
[0361] The transmittance of TiO.sub.2 and Al.sub.2O.sub.3
nanowire-coated ZnS substrates was determined in the visible and
near-IR regions of the spectrum using the protocol described in
Example 15C. The results are reported in the following Table. Each
entry in the Table below is an average of 10 samples.
TABLE-US-00004 TABLE Percent transmittance for bare ZnS, and ZnS
substrates having a ZrO.sub.2 nanowire coating thereon. % T as a
function of Wavelength Sample 1.06 .mu.m 2.5 .mu.m 8-10 .mu.m ZnS
(uncoated) 66% .+-. 1% 79% .+-. 2% 79% .+-. 2% TiO.sub.2 (anatase)
nanowire-coated 66% .+-. 10% 88% .+-. 3% 83% .+-. 2% ZnS TiO.sub.2
(anatase) nanowires 80% .+-. 10% 96% .+-. 4% 83% .+-. 2%
encapsulated on ZnS Al.sub.2O.sub.3 (amorphous) nanowire- 66% .+-.
10% 86% .+-. 4% 82% .+-. 3% coated ZnS Al.sub.2O.sub.3 (amorphous)
nanowires 76% .+-. 10% 95% .+-. 5% 82% .+-. 2% encapsulated in
ZnS
[0362] The transmission properties of the TiO.sub.2 nanowire
coatings and Al.sub.2O.sub.3 nanowire coatings was superior to the
transmission properties of coatings prepared using the much larger
diameter ZrO.sub.2 nanowires. All of the nanowire coatings
exhibited a transmittance greater than 65% at 1.06 .mu.m, with the
encapsulated coatings exhibiting percent transmittance in excess of
75%. Moreover, the percent transmittance for each sample was
greater than 85% at 2.5 .mu.m, and greater than 80% (i.e., 82%-83%)
at 8-10 .mu.m. These results show that the transmittance properties
of the nanowire coatings can be optimized.
Example 17
[0363] The durability and abrasion resistance properties of several
of the coated zinc sulfide (ZnS) substrates prepared in the above
Examples were measured using standard industry protocols. The
substrates and coatings subjected to durability testing were: (a)
uncoated ZnS; (b) ZnS having a thin layer (about 200 nm) of
zirconium oxide thereon (deposited by a sol-gel process); (c); ZnS
having a thin layer (about 200 nm) of styrene-ethylene-butylene
triblock copolymer grafted with maleic anhydride ("SEBMA") thereon;
(d) ZnS having a layer of aligned ZrO.sub.2 nanowires thereon
(deposited for 10 minutes, as in Example 15A to provide a thickness
of about 1.5 .mu.m to about 2 .mu.m); (e) ZnS having thin layer
(about 200 nm) of zirconium oxide thereon followed by a layer of
aligned ZrO.sub.2 nanowires thereon (as in (d)); and (f) ZnS having
a layer of aligned ZrO.sub.2 nanowires thereon (as in (d)),
followed by a thin layer of SEBMA thereon (as in Example 15B).
[0364] The sol-gel zirconia coating was applied by spin-coating a
solution of n-propanol containing 70% by weight zirconia propoxide
at about 500 rpm for about 10 seconds, followed by spinning at
about 1,000 rpm for about 1 minute to dry the layer. Layers of
nanowires could be directly deposited onto the spin-coated, dried
zirconia layer, or the spin-coated, dried zirconia layer was heated
for about 1 hour at about 500.degree. C. in air prior to disposing
a layer of nanowires onto the coated substrate.
[0365] For these tests the thickness of the nanowire coatings was
about 1.5 .mu.m to about 2 .mu.m, the thickness of the zirconium
oxide contact layer was about 200 nm, and the thickness of the
SEBMA was about 200 nm on the substrate, and also coated the
nanowires in a thin polymeric layer. The ZnS substrates were 1'' in
diameter and had a thickness of 0.07''.
[0366] The samples were tested using a "water jet impact test" in
which an aerosol jet of water impinges upon the sample. The samples
were tested using jets of water at velocity intervals of about 100
meters per second (m/sec). Uncoated ZnS samples began to show
damage at about 200 m/sec (which was determined to be the damage
on-set velocity, "DOV," for ZnS). The ZnS having a thin,
sol-gel-derived ZrO.sub.2 coating thereon increased the damage
onset velocity of the ZnS by about 100 m/sec relative to the
uncoated ZnS substrate (i.e., a DOV of about 300 m/sec). However,
the thin layer of ZrO.sub.2 provided little anti-reflection
properties to the ZnS substrate. The SEBMA-coated ZnS substrate
also exhibited a damage onset velocity that was about 100 m/sec
greater than the uncoated ZnS substrate (i.e., a DOV of about 300
m/sec). However, the impact testing caused significant damage to
the polymer coating at the DOV. The ZnS substrates coated with a
layer of aligned ZrO.sub.2 nanowires also exhibited a damage onset
velocity of about 300 msec. The addition of a thin layer of
ZrO.sub.2 between the nanowire layer and the ZnS substrate resulted
in a small increase in the damage onset velocity relative to the
nanowire coating alone. Finally, the composite coatings comprising
a layer of aligned ZrO.sub.2 nanowires and a thin layer of SEBMA
polymer thereon increased the damage onset velocity by about 200
msec (i.e., a DOV of about 400 m/sec), and thus provided the best
durability in the water jet impact tests. However, at a water
velocity of about 400 msec and higher, samples having the thin
layer of ZrO.sub.2 began to delaminate from the ZnS substrate,
whereas the samples having a SEBMA polymer layer deposited thereon
did not suffer from delamination.
[0367] FIGS. 9A-9B provide optical microscope images of an uncoated
ZnS substrate and a ZnS substrate having a layer of aligned
ZrO.sub.2 nanowires thereon, respectively, after water jet impact
testing at a water velocity of about 200 msec. Referring to FIG.
9A, the image, 900, of the uncoated multispectral ZnS substrate,
901, shows extensive damage, 902, after exposure to a water jet at
a velocity of about 200 msec. Referring to FIG. 9B, the image, 910,
of the ZnS substrate coated with a layer of aligned ZrO.sub.2
nanowires thereon (see (d) above), 911, was undamaged by the water
jet at a velocity of 200 msec. Damage induced by the water jet was
limited to superficial damage to the nanowire coating itself, 913,
while the underlying ZnS substrate remained intact.
[0368] As the velocity of the water jet was increased to about 300
msec, the uncoated ZnS substrate underwent even more extensive
damage. FIGS. 9C-9D provide optical microscope images of an
uncoated ZnS substrate and a ZnS substrate having a layer of
aligned ZrO.sub.2 nanowires thereon, respectively, after water jet
impact testing at a water velocity of about 300 msec. Referring to
FIG. 9A, the image, 920, of the uncoated multispectral ZnS
substrate, 921, shows more extensive damage, 922, after exposure to
a water jet at a velocity of about 300 msec. Referring to FIG. 9D,
the image, 930, of the ZnS substrate coated with a layer of aligned
ZrO.sub.2 nanowires thereon (see (d) above), 931, was largely
undamaged by the water jet at a velocity of 300 msec. Damage
induced by the water jet was mainly limited to superficial damage
to the nanowire coating itself, 933, while only a small area of the
underlying ZnS substrate suffered damage, 932.
[0369] At a water jet velocity of about 400 msec, both the uncoated
and nanowire-coated ZnS substrates underwent damage, but again, the
damage to the uncoated ZnS substrate was much more significant.
FIGS. 9E-9F provide optical microscope images of an uncoated ZnS
substrate and a ZnS substrate having a layer of aligned ZrO.sub.2
nanowires thereon, respectively, after water jet impact testing at
a water velocity of about 300 msec. Referring to FIG. 9E, the
image, 940, of the uncoated multispectral ZnS substrate, 941, shows
significant damage, 942, after exposure to a water jet at a
velocity of about 400 msec. Referring to FIG. 9R, the image, 950,
of the ZnS substrate coated with a layer of aligned ZrO.sub.2
nanowires thereon (see (d) above), 951, also shows damage to the
underlying ZnS substrate, 952, as well as areas where only the
ZrO.sub.2 coating was removed from the substrate, 953.
[0370] As shown above, even a single layer of ZrO.sub.2 nanowires
can provide abrasion and water-jet resistance for a ZnS substrate.
The data shows that the damage resistance of the coatings can be
enhanced through the use of a zirconium oxide contact layer and/or
an encapsulant layer that partially encloses the nanowires.
[0371] The durability of the coated ZnS substrates was also tested
using a "falling sand" test, under which conditions the composite
nanowire GRIN coatings of the present invention showed a linear
decrease in transmittance with sand dose. A 1 liter dose of sand
resulted in about a 5% reduction in transmittance, and a 2 liter
dose of sand resulted in about a 10% reduction in transmittance of
the ZnS substrates.
Example 18
[0372] The retro-reflectance properties of several of the coated
substrates prepared in the above Examples were measured using the
experimental arrangement diagrammed schematically in FIG. 10.
Referring to FIG. 10, the apparatus, 1000, included a helium-neon
(He--Ne) laser, 1001 (and 1201-1 power supply, not shown, both from
JDS Uniphase Corp., Milpitas, Calif.), the continuous 633 nm output
(about 4 mW) from which was transmitted through a pinhole, 1002, a
neutral density filter, 1003, a beam expander, 1004, and onto the
sample, 1005. The retro-reflectance intensity was measured using a
photodiode, 1006 (DET10A, Thorlabs, Inc., North Newton, N.J.),
interfaced with an oscilloscope, 1007 (TDS 2002B, Tektronix, Inc.,
Beaverton, Oreg.). The retro-reflection data is summarized in the
following Table.
TABLE-US-00005 TABLE Retro-reflection data for substrates
comprising a nanowire coating of the present invention thereon.
Intensity Relative Substrate Coating (mV) Intensity Silicon None
(Reference) 880 -- Carbon GRIN (5 layers, Example 14) 210 21% ZnO
GRIN (5 layers, Example 8) 400 40% ZrO.sub.2 nanowires (single
layer, 10 min., 68 8% Example 15A) ZrO.sub.2 nanowires,
encapsulated (single layer, 82 9% 10 min., Example 15B) GeO GRIN (5
layers, Example 13) 88 10% Sapphire None (Reference) 700 --
ZrO.sub.2 nanowires (single layer, 10 min., 61 9% Example 15A)
Al.sub.2O.sub.3 GRIN (5 layers, Example 11) 120 17% GeO GRIN (5
layers, Example 13) 72 10% ZnS None (Reference) 635 -- ZrO.sub.2
GRIN (5 layers, Example 9A) 140 22% ZrO.sub.2 nanowires (single
layer, 10 min., 54 9% Example 15A) ZrO.sub.2 nanowires,
encapsulated (single layer, 170 27% 5 min., Example 9A) ZrO.sub.2
nanowires, encapsulated (single layer, 27 4% 10 min., Example 15B)
TiO.sub.2 GRIN encapsulated (5 layers, Example 10) 130 21%
Al.sub.2O.sub.3 GRIN encapsulated (5 layers, Example 11) 120 19%
GeO GRIN encapsulated (5 layers, Example 13) 105 17%
Al.sub.2O.sub.3 encapsulated (1 layer, 16 min, 150 24% Example 11).
Germanium None (Reference) 870 -- ZrO.sub.2 nanowires (single
layer, 10 min., 450 52% Example 15A) GeO GRIN (5 layers, Example
13) 62 7%
[0373] As shown above, all of the nanowire coatings reduce
retro-reflection by at least about 50%. In particular, the
multi-layer GRIN coatings of the present invention reduce
retro-reflectance for silicon, sapphire, zinc sulfide and germanium
substrates by at least about 60% or more. For silicon and sapphire
substrates, GRIN coatings comprising five layers of either
ZrO.sub.2 or GeO nanowires reduced retro-reflectance by about 90%
or more. For a zinc sulfide substrate, a GRIN coating comprising
five layers of ZrO2 nanowires reduced the retro-reflectance by
about 96%. For a germanium substrate, a GRIN coating comprising
five layers of GeO nanowires reduced the retro-reflectance by about
93%. The data shows that the nanowire coatings of the present
invention are suitable for significantly reducing the
retro-reflection for a wide variety of optical materials.
CONCLUSION
[0374] These examples illustrate possible embodiments of the
present invention. While various embodiments of the present
invention have been described above, it should be understood that
they have been presented by way of example only, and not
limitation. It will be apparent to persons skilled in the relevant
art that various changes in form and detail can be made therein
without departing from the spirit and scope of the invention. Thus,
the breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
[0375] It is to be appreciated that the Detailed Description
section, and not the Summary and Abstract sections, is intended to
be used to interpret the claims. The Summary and Abstract sections
can set forth one or more, but not all exemplary embodiments of the
present invention as contemplated by the inventor(s), and thus, are
not intended to limit the present invention and the appended claims
in any way.
[0376] All documents cited herein, including journal articles or
abstracts, published or corresponding U.S. or foreign patent
applications, issued or foreign patents, or any other documents,
are each entirely incorporated by reference herein, including all
data, tables, figures, and text presented in the cited
documents.
* * * * *